[soc2009/multidb] Raise an exception at an attempt to do a subquery with 2 different databases. Eventually we'll just evaluate the 2 queries seperates.

git-svn-id: http://code.djangoproject.com/svn/django/branches/soc2009/multidb@11273 bcc190cf-cafb-0310-a4f2-bffc1f526a37

tests/regressiontests/multiple_database/tests.py

@@ -93,3 +93,5 @@ if len(settings.DATABASES) > 1:
             a.delete()
             self.assertRaises(Article.DoesNotExist,
                 lambda: Article.objects.get(title="Django Rules!"))
+            self.assertRaises(ValueError,
+                lambda: list(Article.objects.get(pk__in=Article.objects.using('default'))))