Django 1.7 regression fixes.

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).
Bump version to 1.5.0a1, and Travis config.