Fix readline detection bug in OSX.

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

Thanks to a patch by Boyd Waters.

IPython/rlineimpl.py

@@ -33,7 +33,19 b" if sys.platform == 'win32' and have_readline:"
 uses_libedit = False
 if sys.platform == 'darwin' and have_readline:
     import commands
+    # 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")