django15 compat
remove custom django-registration 0.8 backend

we've upgraded to django registration 1.0 because of the
django 1.5 upgrade and 1.0 uses CVBs instead of a backend
Merge remote-tracking branch 'upstream/master' into registration_tests
Merge pull request #8 from RaphaelKimmig/registration_tests

Django 1.5 compatibility