do tab-completion on OS-X stock python too (libedit)

Apple's stock python doesn't use GNU libreadline, instead it uses BSD
libedit with a readline compatibility interface. The syntax to enable
tab completion is different for libedit. By including both bindings,
autocomplete should work on both flavors.

Closes #37. Thanks to @wsanchez for the catch and the fix.

src/wormhole/codes.py

@@ -88,6 +88,7 @@ def input_code_with_completion(prompt, initial_channelids, get_channel_ids,
         import readline
         c = CodeInputter(initial_channelids, get_channel_ids, code_length)
         readline.parse_and_bind("tab: complete")
+        readline.parse_and_bind("bind ^I rl_complete")
         readline.set_completer(c.wrap_completer)
         readline.set_completer_delims("")
     except ImportError: