major refactor of the tests:
* moves tests package to root of project and renames it to test_django_filters
* splits tests.py into multiple files
* removes fixture need by creating instances on the fly
** attempted to use factory_boy instead, but it isn't py3k compatible yet
* uses django-discover-runner to find the test cases

while primarily focused on test refactoring, it also:
* updates runtests.py to allow more flexibility when running tests
* adds a runshell.py which configures django, runs syncdb and loads the test environment shell (in-memory sqlite db)
* adds pip requirements files for new test dependencies
* updates MANIFEST.in for test package split
* uses py3k compatible relative imports when possible
* removes XMLField handling, since we only support Django >= 1.4
* removes unnecessary code to get length on MultipleChoiceField's choices when filtering
* updates code for pep8 and pyflakes adherence
update travis.yml for 1.5rc2 and 1.4.4 bugfix versions of Django
update travis.yml for 1.4.5 release version of Django
add coverage.py for travis tests and some import/pep8 cleanup
added new tests and refactored some previous tests
* removed tests that essentially covered form/field rendering
* added more edge-case tests (Proxy models, MTI models, filtering through relationships)
* moved most of the tests which performed queryset filtering to new filtering_tests.py
* added "pragma: nocover" in a few places for coverage.py to omit for reporting
* included fix for generic view error inside of ImproperlyConfigured handler
Updates travis yaml for Django 1.5 and also includes Django master branch now.
Some tests needed explicit non-ordering set, because Django 1.6 raises
ValueError when using assertQuerySetEqual without it.  Also, needed to add
a couple skipIf/skipUnless to handle Django 1.6 using html5 input types.
Merge pull request #79 from nkryptic/tests-refactor-plus-cleanup

major refactor of the tests, plus some cleanup