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.
Merge pull request #9 from lukesneeringer/django-1.7-unstable

Fix Django 1.7 regressions.