Made `with` statements added in [16348] compatible with Python 2.5.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@16357 bcc190cf-cafb-0310-a4f2-bffc1f526a37

tests/modeltests/validation/test_unique.py

@@ -1,3 +1,5 @@
+from __future__ import with_statement
+
 import datetime
 
 from django.conf import settings
@@ -143,4 +145,4 @@ class PerformUniqueChecksTest(TestCase):
         with self.assertRaises(ValidationError) as cm:
             m.full_clean()
         self.assertEqual(cm.exception.message_dict, {'number': [u'Custom unique number message.']})
-            
+