Run django.setup() before tests for Django >= 1.7.

To run the tests with Django-1.7 you need to call django.setup() before anything
wants to access the App registry in a standalone script. See
https://docs.djangoproject.com/en/dev/releases/1.7/#standalone-scripts for
details.
This import, like the other django imports should be withing the ``runtests`` function.