[1.1.X] Fixed #12858. DateTime related widgets now handle custom formats...

[1.1.X] Fixed #12858. DateTime related widgets now handle custom formats properly in _has_changed. Backport of r12698 from trunk.


git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.1.X@12699 bcc190cf-cafb-0310-a4f2-bffc1f526a37