Django 1.5 and max possible z-index

    * Added support for Django 1.5
    * Bumbped the z-index value to max possible.
Merge pull request #8 from owais/master

Support for Django 1.5 and max possible z-index
merge remote-tracking branch 'upstream/master'

Merge upstream changes from https://github.com/ikraft/django-userswitch to support custom User model from Django 1.5.

Conflicts:
	README.rst
	setup.py
	userswitch/middleware.py