[1.0.X] Fixed #10288 -- Corrected _has_changed handling of DateTimeInput when...

[1.0.X] Fixed #10288 -- Corrected _has_changed handling of DateTimeInput when a custom date/time format is in use. Thanks to Koen Biermans for the report and patch.

Merge of r10641 from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.0.X@10757 bcc190cf-cafb-0310-a4f2-bffc1f526a37