fix symlinked /home issue for FreeBSD

this is a one-line fix for ipython's pushd and friends on systems which
symlink /home directories to /usr/home. Here's the error I get on
FreeBSD 9.0 without this PR:

======================================================================
FAIL: Test various directory handling operations.
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/usr/local/lib/python2.7/site-packages/nose-1.1.2-py2.7.egg/nose/case.py", line 197, in runTest
    self.test(*self.arg)
  File "/usr/home/pi/code/ipython/IPython/core/tests/test_magic.py", line 280, in test_dirops
    nt.assert_equal(curpath(), startdir)
AssertionError: u'/usr/home/pi/.ipython' != u'/usr/home/pi/code/ipython'
- /usr/home/pi/.ipython
?              ^
+ /usr/home/pi/code/ipython
?              ^^^^^

    """Fail immediately, with the given message."""
>>  raise self.failureException(u"u'/usr/home/pi/.ipython' != u'/usr/home/pi/code/ipython'\n- /usr/home/pi/.ipython\n?              ^\n+ /usr/home/pi/code/ipython\n?              ^^^^^\n")

-------------------- >> begin captured stdout << ---------------------
/usr/home/pi/.ipython
/usr/home/pi/code/ipython
/usr/home/pi/.ipython
[Errno 2] No such file or directory: '/usr~/code/ipython'
/usr/home/pi/.ipython
popd -> /usr~/code/ipython

--------------------- >> end captured stdout << ----------------------

The reason for the above is this:

In [1]: pwd
Out[1]: u'/usr/home/pi'

In [2]: !pwd
/home/pi

In [3]: pushd code
/usr/home/pi/code
Out[3]: [u'/usr~']

with this commit:

In [1]: pushd
Out[1]: [u'~']

IPython/utils/path.py

@@ -1,461 +1,464 b''
 # encoding: utf-8
 """
 Utilities for path handling.
 """
 
 #-----------------------------------------------------------------------------
 #  Copyright (C) 2008-2011  The IPython Development Team
 #
 #  Distributed under the terms of the BSD License.  The full license is in
 #  the file COPYING, distributed as part of this software.
 #-----------------------------------------------------------------------------
 
 #-----------------------------------------------------------------------------
 # Imports
 #-----------------------------------------------------------------------------
 
 import os
 import sys
 import tempfile
 import warnings
 from hashlib import md5
 
 import IPython
 from IPython.utils.process import system
 from IPython.utils.importstring import import_item
 from IPython.utils import py3compat
 
 #-----------------------------------------------------------------------------
 # Code
 #-----------------------------------------------------------------------------
 
 fs_encoding = sys.getfilesystemencoding()
 
 def _get_long_path_name(path):
     """Dummy no-op."""
     return path
 
 def _writable_dir(path):
     """Whether `path` is a directory, to which the user has write access."""
     return os.path.isdir(path) and os.access(path, os.W_OK)
 
 if sys.platform == 'win32':
     def _get_long_path_name(path):
         """Get a long path name (expand ~) on Windows using ctypes.
 
         Examples
         --------
 
         >>> get_long_path_name('c:\\docume~1')
         u'c:\\\\Documents and Settings'
 
         """
         try:
             import ctypes
         except ImportError:
             raise ImportError('you need to have ctypes installed for this to work')
         _GetLongPathName = ctypes.windll.kernel32.GetLongPathNameW
         _GetLongPathName.argtypes = [ctypes.c_wchar_p, ctypes.c_wchar_p,
             ctypes.c_uint ]
 
         buf = ctypes.create_unicode_buffer(260)
         rv = _GetLongPathName(path, buf, 260)
         if rv == 0 or rv > 260:
             return path
         else:
             return buf.value
 
 
 def get_long_path_name(path):
     """Expand a path into its long form.
 
     On Windows this expands any ~ in the paths. On other platforms, it is
     a null operation.
     """
     return _get_long_path_name(path)
 
 
 def unquote_filename(name, win32=(sys.platform=='win32')):
     """ On Windows, remove leading and trailing quotes from filenames.
     """
     if win32:
         if name.startswith(("'", '"')) and name.endswith(("'", '"')):
             name = name[1:-1]
     return name
 
 
 def get_py_filename(name, force_win32=None):
     """Return a valid python filename in the current directory.
 
     If the given name is not a file, it adds '.py' and searches again.
     Raises IOError with an informative message if the file isn't found.
 
     On Windows, apply Windows semantics to the filename. In particular, remove
     any quoting that has been applied to it. This option can be forced for
     testing purposes.
     """
 
     name = os.path.expanduser(name)
     if force_win32 is None:
         win32 = (sys.platform == 'win32')
     else:
         win32 = force_win32
     name = unquote_filename(name, win32=win32)
     if not os.path.isfile(name) and not name.endswith('.py'):
         name += '.py'
     if os.path.isfile(name):
         return name
     else:
         raise IOError,'File `%s` not found.' % name
 
 
 def filefind(filename, path_dirs=None):
     """Find a file by looking through a sequence of paths.
 
     This iterates through a sequence of paths looking for a file and returns
     the full, absolute path of the first occurence of the file.  If no set of
     path dirs is given, the filename is tested as is, after running through
     :func:`expandvars` and :func:`expanduser`.  Thus a simple call::
 
         filefind('myfile.txt')
 
     will find the file in the current working dir, but::
 
         filefind('~/myfile.txt')
 
     Will find the file in the users home directory.  This function does not
     automatically try any paths, such as the cwd or the user's home directory.
 
     Parameters
     ----------
     filename : str
         The filename to look for.
     path_dirs : str, None or sequence of str
         The sequence of paths to look for the file in.  If None, the filename
         need to be absolute or be in the cwd.  If a string, the string is
         put into a sequence and the searched.  If a sequence, walk through
         each element and join with ``filename``, calling :func:`expandvars`
         and :func:`expanduser` before testing for existence.
 
     Returns
     -------
     Raises :exc:`IOError` or returns absolute path to file.
     """
 
     # If paths are quoted, abspath gets confused, strip them...
     filename = filename.strip('"').strip("'")
     # If the input is an absolute path, just check it exists
     if os.path.isabs(filename) and os.path.isfile(filename):
         return filename
 
     if path_dirs is None:
         path_dirs = ("",)
     elif isinstance(path_dirs, basestring):
         path_dirs = (path_dirs,)
 
     for path in path_dirs:
         if path == '.': path = os.getcwdu()
         testname = expand_path(os.path.join(path, filename))
         if os.path.isfile(testname):
             return os.path.abspath(testname)
 
     raise IOError("File %r does not exist in any of the search paths: %r" %
                   (filename, path_dirs) )
 
 
 class HomeDirError(Exception):
     pass
 
 
 def get_home_dir(require_writable=False):
     """Return the 'home' directory, as a unicode string.
 
     * First, check for frozen env in case of py2exe
     * Otherwise, defer to os.path.expanduser('~')
     
     See stdlib docs for how this is determined.
     $HOME is first priority on *ALL* platforms.
     
     Parameters
     ----------
     
     require_writable : bool [default: False]
         if True:
             guarantees the return value is a writable directory, otherwise
             raises HomeDirError
         if False:
             The path is resolved, but it is not guaranteed to exist or be writable.
     """
 
     # first, check py2exe distribution root directory for _ipython.
     # This overrides all. Normally does not exist.
 
     if hasattr(sys, "frozen"): #Is frozen by py2exe
         if '\\library.zip\\' in IPython.__file__.lower():#libraries compressed to zip-file
             root, rest = IPython.__file__.lower().split('library.zip')
         else:
             root=os.path.join(os.path.split(IPython.__file__)[0],"../../")
         root=os.path.abspath(root).rstrip('\\')
         if _writable_dir(os.path.join(root, '_ipython')):
             os.environ["IPYKITROOT"] = root
         return py3compat.cast_unicode(root, fs_encoding)
     
     homedir = os.path.expanduser('~')
+    # Next line will make things work even when /home/ is a symlink to
+    # /usr/home as it is on FreeBSD, for example
+    homedir = os.path.realpath(homedir)
     
     if not _writable_dir(homedir) and os.name == 'nt':
         # expanduser failed, use the registry to get the 'My Documents' folder.
         try:
             import _winreg as wreg
             key = wreg.OpenKey(
                 wreg.HKEY_CURRENT_USER,
                 "Software\Microsoft\Windows\CurrentVersion\Explorer\Shell Folders"
             )
             homedir = wreg.QueryValueEx(key,'Personal')[0]
             key.Close()
         except:
             pass
     
     if (not require_writable) or _writable_dir(homedir):
         return py3compat.cast_unicode(homedir, fs_encoding)
     else:
         raise HomeDirError('%s is not a writable dir, '
                 'set $HOME environment variable to override' % homedir)
 
 def get_xdg_dir():
     """Return the XDG_CONFIG_HOME, if it is defined and exists, else None.
 
     This is only for posix (Linux,Unix,OS X, etc) systems.
     """
 
     env = os.environ
 
     if os.name == 'posix':
         # Linux, Unix, AIX, OS X
         # use ~/.config if empty OR not set
         xdg = env.get("XDG_CONFIG_HOME", None) or os.path.join(get_home_dir(), '.config')
         if xdg and _writable_dir(xdg):
             return py3compat.cast_unicode(xdg, fs_encoding)
 
     return None
 
 
 def get_ipython_dir():
     """Get the IPython directory for this platform and user.
 
     This uses the logic in `get_home_dir` to find the home directory
     and then adds .ipython to the end of the path.
     """
 
     env = os.environ
     pjoin = os.path.join
 
 
     ipdir_def = '.ipython'
     xdg_def = 'ipython'
 
     home_dir = get_home_dir()
     xdg_dir = get_xdg_dir()
     
     # import pdb; pdb.set_trace()  # dbg
     ipdir = env.get('IPYTHON_DIR', env.get('IPYTHONDIR', None))
     if ipdir is None:
         # not set explicitly, use XDG_CONFIG_HOME or HOME
         home_ipdir = pjoin(home_dir, ipdir_def)
         if xdg_dir:
             # use XDG, as long as the user isn't already
             # using $HOME/.ipython and *not* XDG/ipython
 
             xdg_ipdir = pjoin(xdg_dir, xdg_def)
 
             if _writable_dir(xdg_ipdir) or not _writable_dir(home_ipdir):
                 ipdir = xdg_ipdir
 
         if ipdir is None:
             # not using XDG
             ipdir = home_ipdir
 
     ipdir = os.path.normpath(os.path.expanduser(ipdir))
 
     if os.path.exists(ipdir) and not _writable_dir(ipdir):
         # ipdir exists, but is not writable
         warnings.warn("IPython dir '%s' is not a writable location,"
                         " using a temp directory."%ipdir)
         ipdir = tempfile.mkdtemp()
     elif not os.path.exists(ipdir):
         parent = ipdir.rsplit(os.path.sep, 1)[0]
         if not _writable_dir(parent):
             # ipdir does not exist and parent isn't writable
             warnings.warn("IPython parent '%s' is not a writable location,"
                         " using a temp directory."%parent)
             ipdir = tempfile.mkdtemp()
 
     return py3compat.cast_unicode(ipdir, fs_encoding)
 
 
 def get_ipython_package_dir():
     """Get the base directory where IPython itself is installed."""
     ipdir = os.path.dirname(IPython.__file__)
     return py3compat.cast_unicode(ipdir, fs_encoding)
 
 
 def get_ipython_module_path(module_str):
     """Find the path to an IPython module in this version of IPython.
 
     This will always find the version of the module that is in this importable
     IPython package. This will always return the path to the ``.py``
     version of the module.
     """
     if module_str == 'IPython':
         return os.path.join(get_ipython_package_dir(), '__init__.py')
     mod = import_item(module_str)
     the_path = mod.__file__.replace('.pyc', '.py')
     the_path = the_path.replace('.pyo', '.py')
     return py3compat.cast_unicode(the_path, fs_encoding)
 
 def locate_profile(profile='default'):
     """Find the path to the folder associated with a given profile.
     
     I.e. find $IPYTHON_DIR/profile_whatever.
     """
     from IPython.core.profiledir import ProfileDir, ProfileDirError
     try:
         pd = ProfileDir.find_profile_dir_by_name(get_ipython_dir(), profile)
     except ProfileDirError:
         # IOError makes more sense when people are expecting a path
         raise IOError("Couldn't find profile %r" % profile)
     return pd.location
 
 def expand_path(s):
     """Expand $VARS and ~names in a string, like a shell
 
     :Examples:
 
        In [2]: os.environ['FOO']='test'
 
        In [3]: expand_path('variable FOO is $FOO')
        Out[3]: 'variable FOO is test'
     """
     # This is a pretty subtle hack. When expand user is given a UNC path
     # on Windows (\\server\share$\%username%), os.path.expandvars, removes
     # the $ to get (\\server\share\%username%). I think it considered $
     # alone an empty var. But, we need the $ to remains there (it indicates
     # a hidden share).
     if os.name=='nt':
         s = s.replace('$\\', 'IPYTHON_TEMP')
     s = os.path.expandvars(os.path.expanduser(s))
     if os.name=='nt':
         s = s.replace('IPYTHON_TEMP', '$\\')
     return s
 
 
 def target_outdated(target,deps):
     """Determine whether a target is out of date.
 
     target_outdated(target,deps) -> 1/0
 
     deps: list of filenames which MUST exist.
     target: single filename which may or may not exist.
 
     If target doesn't exist or is older than any file listed in deps, return
     true, otherwise return false.
     """
     try:
         target_time = os.path.getmtime(target)
     except os.error:
         return 1
     for dep in deps:
         dep_time = os.path.getmtime(dep)
         if dep_time > target_time:
             #print "For target",target,"Dep failed:",dep # dbg
             #print "times (dep,tar):",dep_time,target_time # dbg
             return 1
     return 0
 
 
 def target_update(target,deps,cmd):
     """Update a target with a given command given a list of dependencies.
 
     target_update(target,deps,cmd) -> runs cmd if target is outdated.
 
     This is just a wrapper around target_outdated() which calls the given
     command if target is outdated."""
 
     if target_outdated(target,deps):
         system(cmd)
 
 def filehash(path):
     """Make an MD5 hash of a file, ignoring any differences in line
     ending characters."""
     with open(path, "rU") as f:
         return md5(py3compat.str_to_bytes(f.read())).hexdigest()
 
 # If the config is unmodified from the default, we'll just delete it.
 # These are consistent for 0.10.x, thankfully. We're not going to worry about
 # older versions.
 old_config_md5 = {'ipy_user_conf.py': 'fc108bedff4b9a00f91fa0a5999140d3',
                   'ipythonrc': '12a68954f3403eea2eec09dc8fe5a9b5'}
 
 def check_for_old_config(ipython_dir=None):
     """Check for old config files, and present a warning if they exist.
 
     A link to the docs of the new config is included in the message.
 
     This should mitigate confusion with the transition to the new
     config system in 0.11.
     """
     if ipython_dir is None:
         ipython_dir = get_ipython_dir()
 
     old_configs = ['ipy_user_conf.py', 'ipythonrc', 'ipython_config.py']
     warned = False
     for cfg in old_configs:
         f = os.path.join(ipython_dir, cfg)
         if os.path.exists(f):
             if filehash(f) == old_config_md5.get(cfg, ''):
                 os.unlink(f)
             else:
                 warnings.warn("Found old IPython config file %r (modified by user)"%f)
                 warned = True
 
     if warned:
         warnings.warn("""
   The IPython configuration system has changed as of 0.11, and these files will
   be ignored. See http://ipython.github.com/ipython-doc/dev/config for details
   of the new config system.
   To start configuring IPython, do `ipython profile create`, and edit
   `ipython_config.py` in <ipython_dir>/profile_default.
   If you need to leave the old config files in place for an older version of
   IPython and want to suppress this warning message, set
   `c.InteractiveShellApp.ignore_old_config=True` in the new config.""")
 
 def get_security_file(filename, profile='default'):
     """Return the absolute path of a security file given by filename and profile
     
     This allows users and developers to find security files without
     knowledge of the IPython directory structure. The search path
     will be ['.', profile.security_dir]
     
     Parameters
     ----------
     
     filename : str
         The file to be found. If it is passed as an absolute path, it will
         simply be returned.
     profile : str [default: 'default']
         The name of the profile to search.  Leaving this unspecified
         The file to be found. If it is passed as an absolute path, fname will
         simply be returned.
     
     Returns
     -------
     Raises :exc:`IOError` if file not found or returns absolute path to file.
     """
     # import here, because profiledir also imports from utils.path
     from IPython.core.profiledir import ProfileDir
     try:
         pd = ProfileDir.find_profile_dir_by_name(get_ipython_dir(), profile)
     except Exception:
         # will raise ProfileDirError if no such profile
         raise IOError("Profile %r not found")
     return filefind(filename, ['.', pd.security_dir])