Fixed `GeoManager.get_query_set` incompatibility with `db_manager` method.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@12021 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/contrib/gis/db/models/manager.py

@@ -10,7 +10,10 @@ class GeoManager(Manager):
     use_for_related_fields = True
 
     def get_query_set(self):
-        return GeoQuerySet(model=self.model)
+        qs = GeoQuerySet(self.model)
+        if self._db is not None:
+            qs = qs.using(self._db)
+        return qs
 
     def area(self, *args, **kwargs):
         return self.get_query_set().area(*args, **kwargs)