Fixed #3247 -- newforms form_for_model() and form_for_instance() no longer create form fields for database fields with editable=False. Thanks for the patch, mssnlayam@yahoo.com and Philipp Keller

git-svn-id: http://code.djangoproject.com/svn/django/trunk@4548 bcc190cf-cafb-0310-a4f2-bffc1f526a37