Changed the default form presentation of datetime values to not include the

fractional second values (they usually aren't going to be needed). Based on
patches from yi.codeplayer@gmail.com, andrews and Wiliam Alves de Souza. Fixed #4428, #4487


git-svn-id: http://code.djangoproject.com/svn/django/trunk@6578 bcc190cf-cafb-0310-a4f2-bffc1f526a37