Update form.php - see bug tracker 31059 for more detail and test case

Fix the "attribs" value to allow using the loadForm() and bind() on the attributes like in the back-end.

Reported in bug tracker 31059
http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_id=8103&tracker_item_id=31059