[1.2.X] Modified a few tests methods to make sure no leaks of activated locale...

[1.2.X] Modified a few tests methods to make sure no leaks of activated locale or USE_L10N setting value happen between tests.

Backport of [15411] from trunk

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@15412 bcc190cf-cafb-0310-a4f2-bffc1f526a37