add `-a` to easy_install command in libedit warning

needed if someone has accidentally installed with pip,
in which case `easy_install readline` is a no-op.

IPython/utils/rlineimpl.py

@@ -1,107 +1,107 b''
 # -*- coding: utf-8 -*-
 """ Imports and provides the 'correct' version of readline for the platform.
 
 Readline is used throughout IPython as::
 
     import IPython.utils.rlineimpl as readline
 
 In addition to normal readline stuff, this module provides have_readline
 boolean and _outputfile variable used in IPython.utils.
 """
 
 import sys
 import warnings
 
 if sys.platform == 'darwin':
     # dirty trick, to skip the system readline, because pip-installed readline
     # will never be found on OSX, since lib-dynload always comes ahead of site-packages
     from distutils import sysconfig
     lib_dynload = sysconfig.get_config_var('DESTSHARED')
     del sysconfig
     try:
         dynload_idx = sys.path.index(lib_dynload)
     except ValueError:
         dynload_idx = None
     else:
         sys.path.pop(dynload_idx)
 try:
     from readline import *
     import readline as _rl
     have_readline = True
 except ImportError:
     try:
         from pyreadline import *
         import pyreadline as _rl
         have_readline = True
     except ImportError:
         have_readline = False
 
 if sys.platform == 'darwin':
     # dirty trick, part II:
     if dynload_idx is not None:
         # restore path
         sys.path.insert(dynload_idx, lib_dynload)
         if not have_readline:
             # *only* have system readline, try import again
             try:
                 from readline import *
                 import readline as _rl
                 have_readline = True
             except ImportError:
                 have_readline = False
             else:
                 # if we want to warn about EPD / Fink having bad readline
                 # we would do it here
                 pass
     # cleanup dirty trick vars
     del dynload_idx, lib_dynload
 
 if (sys.platform == 'win32' or sys.platform == 'cli') and have_readline:
     try:
         _outputfile=_rl.GetOutputFile()
     except AttributeError:
         warnings.warn("Failed GetOutputFile")
         have_readline = False
 
 # Test to see if libedit is being used instead of GNU readline.
 # Thanks to Boyd Waters for the original patch.
 uses_libedit = False
 
 if have_readline:
     # Official Python docs state that 'libedit' is in the docstring for libedit readline:
     uses_libedit = _rl.__doc__ and 'libedit' in _rl.__doc__
     # Note that many non-System Pythons also do not use proper readline,
     # but do not report libedit at all, nor are they linked dynamically against libedit.
     # known culprits of this include: EPD, Fink
     # There is not much we can do to detect this, until we find a specific failure
     # case, rather than relying on the readline module to self-identify as broken.
 
 if uses_libedit and sys.platform == 'darwin':
     _rl.parse_and_bind("bind ^I rl_complete")
     warnings.warn('\n'.join(['', "*"*78,
         "libedit detected - readline will not be well behaved, including but not limited to:",
         "   * crashes on tab completion",
         "   * incorrect history navigation",
         "   * corrupting long-lines",
         "   * failure to wrap or indent lines properly",
         "It is highly recommended that you install readline, which is easy_installable:",
-        "     easy_install readline",
+        "     easy_install -a readline",
         "Note that `pip install readline` generally DOES NOT WORK, because",
         "it installs to site-packages, which come *after* lib-dynload in sys.path,",
-        "where readline is located.  It must be `easy_install readline`, or to a custom",
+        "where readline is located.  It must be `easy_install -a readline`, or to a custom",
         "location on your PYTHONPATH (even --user comes after lib-dyload).",
         "*"*78]),
         RuntimeWarning)
 
 # the clear_history() function was only introduced in Python 2.4 and is
 # actually optional in the readline API, so we must explicitly check for its
 # existence.  Some known platforms actually don't have it.  This thread:
 # http://mail.python.org/pipermail/python-dev/2003-August/037845.html
 # has the original discussion.
 
 if have_readline:
     try:
         _rl.clear_history
     except AttributeError:
         def clear_history(): pass
         _rl.clear_history = clear_history