Fixed a bug that appears by using the bash autocompletion with Python 3.

The bug happened by using the django autocompletion after a command:

    $ django-admin startproject Traceback (most recent call last):
          ...
      File ".../django/core/management/__init__.py", line 262, in autocomplete
        options = sorted((k, v) for k, v in options if k.startswith(curr))
    TypeError: unorderable types: bool() < NoneType()