[1.5.x] Removed implication that six is part of Python stdlib.

~~~~~~~~~~~~~

Some modules were renamed in Python 3. The ``django.utils.six.moves``

module (based on the :mod:`Python six.moves module <six.moves>`) provides a

module (based on the :mod:`six.moves module <six.moves>`) provides a

compatible location to import them.

The ``urllib``, ``urllib2`` and ``urlparse`` modules were reworked in depth