fallback on lsof if otool not found in libedit detection

This is necessary for Macs without XCode.
It also prevents a crash in the unlikely event that neither is found.
lsof detection is vulnerable to false positives if other (non-readline)
modules are linked against libedit, but this is also unlikely.

closes gh-524

IPython/utils/rlineimpl.py

@@ -1,95 +1,112 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 os
 import re
 import sys
 import time
 import warnings
 
 from subprocess import Popen, PIPE
 
 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 have_readline and hasattr(_rl, 'rlmain'):
     # patch add_history to allow for strings in pyreadline <= 1.5:
     # fix copied from pyreadline 1.6
     import pyreadline
     if pyreadline.release.version <= '1.5':
         def add_history(line):
             """add a line to the history buffer."""
             from pyreadline import lineobj
             if not isinstance(line, lineobj.TextLine):
                 line = lineobj.TextLine(line)
             return _rl.add_history(line)
 
 if sys.platform == 'win32' and have_readline:
     try:
         _outputfile=_rl.GetOutputFile()
     except AttributeError:
         print "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 sys.platform == 'darwin' and have_readline:
     # Previously this used commands.getstatusoutput, which uses os.popen.
     # Switching to subprocess.Popen, and exponential falloff for EINTR
     # seems to make this better behaved in environments such as PyQt and gdb
     dt = 1e-3
     while dt < 1:
-        p = Popen(['otool', '-L', _rl.__file__], stdout=PIPE, stderr=PIPE)
-        otool,err = p.communicate()
+        try:
+            p = Popen(['otool', '-L', _rl.__file__], stdout=PIPE, stderr=PIPE)
+        except OSError:
+            try:
+                # otool not available (no XCode), use lsof instead.
+                # This *could* have a false positive
+                # if another package that uses libedit explicitly
+                # has been imported prior to this test.
+                p = Popen(['lsof', '-p', str(os.getpid())], stdout=PIPE, stderr=PIPE)
+            except OSError:
+                # This is highly unlikely, but let's be sure
+                # we don't crash IPython just because we can't find lsof
+                p = out = err = None
+                warnings.warn("libedit detection failed")
+                break
+
+        out,err = p.communicate()
 
         if p.returncode == 4:
             # EINTR
             time.sleep(dt)
             dt *= 2
             continue
-        elif p.returncode:
+        elif p is None or p.returncode:
             warnings.warn("libedit detection failed: %s"%err)
             break
         else:
             break
 
-    if p.returncode == 0 and re.search(r'/libedit[\.\d+]*\.dylib\s', otool):
+    if p is not None and p.returncode == 0 and re.search(r'/libedit[\.\d+]*\.dylib\s', out):
         # we are bound to libedit - new in Leopard
         _rl.parse_and_bind("bind ^I rl_complete")
         warnings.warn("Leopard libedit detected - readline will not be well behaved "
             "including some crashes on tab completion, and incorrect history navigation. "
             "It is highly recommended that you install readline, "
             "which is easy_installable with: 'easy_install readline'",
             RuntimeWarning)
         uses_libedit = True
-
+    # cleanup names
+    del dt,p,out,err
 
 # 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