[1.0.X] 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.

Backport of r9206 from trunk.


git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.0.X@9207 bcc190cf-cafb-0310-a4f2-bffc1f526a37

tests/regressiontests/queries/models.py

@@ -973,6 +973,12 @@ Make sure bump_prefix() (an internal Query method) doesn't (re-)break.
 >>> query.bump_prefix()
 >>> print query.as_sql()[0]
 SELECT U0."id" FROM "queries_tag" U0
+
+Calling order_by() with no parameters removes any existing ordering on the
+model. But it should still be possible to add new ordering after that.
+>>> qs = Author.objects.order_by().order_by('name')
+>>> 'ORDER BY' in qs.query.as_sql()[0]
+True
 """}
 
 # In Python 2.3 and the Python 2.6 beta releases, exceptions raised in __len__