[1.0.X] Fixed #9520: make the date filter fail silently for non-date values....

[1.0.X] Fixed #9520: make the date filter fail silently for non-date values. Thanks, Andrew Badr and Eric Holscher. Backport of r10365 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.0.X@10366 bcc190cf-cafb-0310-a4f2-bffc1f526a37