Fixed #13621 -- Corrected the handling of input formats on date/time form fields. Thanks to bufke for the report, zerok and jacmkno for their work on the patch, and Karen, Jannis and Alex for feedback.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@13484 bcc190cf-cafb-0310-a4f2-bffc1f526a37