Fixed #2098 -- Loosened validation for model 'ordering' parameter by allowing...

Fixed #2098 -- Loosened validation for model 'ordering' parameter by allowing periods. Thanks, Alex Dedul

git-svn-id: http://code.djangoproject.com/svn/django/trunk@3095 bcc190cf-cafb-0310-a4f2-bffc1f526a37