[1.2.X] Ensure the mutliple_database tests leave the settings in the same...

[1.2.X] Ensure the mutliple_database tests leave the settings in the same state they found them.  Backport of [14313].

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@14314 bcc190cf-cafb-0310-a4f2-bffc1f526a37