Custom User Model for Django 1.5
Fixing warning which prevented tests from succeeding

Now that we're importing the auth classes in the tests, no warning can be
raised or test_dbref_reference_field_future_warning will fail.
Tests should not require Django 1.5 to run
Travis: adding Django-1.5.1 to env
Auth cleanups - removed duplicates
Merge remote-tracking branch 'origin/pr/285' into p285
Upgrade changelog, docs and django/auth.py