[1.2.X] Fixed #13062 -- Ensure that runserver exposes all warnings requested...

[1.2.X] Fixed #13062 -- Ensure that runserver exposes all warnings requested at the command line. Thanks to gremmie for the report, and claudep for the patch.

Backport of r15233 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@15234 bcc190cf-cafb-0310-a4f2-bffc1f526a37