Corrected the setup and teardown of the refactored invalid_models test so that...

Corrected the setup and teardown of the refactored invalid_models test so that it guarantees that stdout is restored, and purges all the temporary models from the app cache after running the test.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@16670 bcc190cf-cafb-0310-a4f2-bffc1f526a37