Fix Django 1.7 regressions.

This commit does everything necessary to get current functionality (sans South support) working in Django 1.7.

This includes:

  * Using the new lookups system when Django 1.7 is in use.
  * Updating the call signature of `Query` and `GeoQuery`.
  * Updating the test runner to run `django.setup()` if possible.

This does **not** add support for Django 1.7 stock migrations, and using South probably does not work (it bombs when tested).