[1.3.X] Corrected the setup and teardown of the refactored invalid_models test...

[1.3.X] 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.

Backport of r16670 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.3.X@16677 bcc190cf-cafb-0310-a4f2-bffc1f526a37