Fix readline detection bug in OSX.

Close https://bugs.launchpad.net/ipython/+bug/411599

Thanks to a patch by Boyd Waters.

IPython/rlineimpl.py

@@ -1,55 +1,67 b''
 # -*- coding: utf-8 -*-
 """ Imports and provides the 'correct' version of readline for the platform.
 
 Readline is used throughout IPython as 'import IPython.rlineimpl as readline'.
 
 In addition to normal readline stuff, this module provides have_readline
 boolean and _outputfile variable used in genutils.
 """
 
 import sys
 
 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 == '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 this patch.
 uses_libedit = False
 if sys.platform == 'darwin' and have_readline:
     import commands
-    (status, result) = commands.getstatusoutput( "otool -L %s | grep libedit" % _rl.__file__ )
+    # Boyd's patch had a 'while True' here, I'm always a little worried about
+    # infinite loops with such code, so for now I'm taking a more conservative
+    # approach. See https://bugs.launchpad.net/ipython/+bug/411599.
+    for i in range(10):
+        try:
+            (status, result) = commands.getstatusoutput( "otool -L %s | grep libedit" % _rl.__file__ )
+            break
+        except IOError, (errno, strerror):
+            if errno == 4:
+                continue
+            else
+                break
+
     if status == 0 and len(result) > 0:
         # we are bound to libedit - new in Leopard
         _rl.parse_and_bind("bind ^I rl_complete")
         print "Leopard libedit detected."
         uses_libedit = True
 
 
 # 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