South migration uses get_auth_model

Using get_auth_model gives south the _currently_ configured AUTH_USER_MODEL.
This works fine for new initial database migrations, but it will fail when
AUTH_USER_MODEL changes over the lifetime of a django DB.
not zip_safe and version bump

not zip_safe becasue manage.py migrate complained about not finding the
migration file
Merge pull request #3 from daniel-treparel/master

South migration uses get_auth_model