Fixed #11842 -- django-admin.py now displays usage information if invoked with...

Fixed #11842 -- django-admin.py now displays usage information if invoked with no arguments. Thanks, bitprophet

git-svn-id: http://code.djangoproject.com/svn/django/trunk@12198 bcc190cf-cafb-0310-a4f2-bffc1f526a37