A queryset that has had ordering removed (order_by()) can have ordering added

again later (order_by('foo')). Or, at least, it can now. Thanks to Ilya
Novoselov for diagnosing the problem here.


git-svn-id: http://code.djangoproject.com/svn/django/trunk@9206 bcc190cf-cafb-0310-a4f2-bffc1f526a37