GeoDjango test suite housekeeping. Moved data into fixtures for `relatedapp`...

GeoDjango test suite housekeeping.  Moved data into fixtures for `relatedapp` and `distapp` tests, and made both use Django's `TestCase`; moved functionality out of `GeoDjangoTestSuiteRunner` to allow future re-use in `runtests.py` (refs #10420); compressed test app fixtures and cleaned up imports.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@14776 bcc190cf-cafb-0310-a4f2-bffc1f526a37