[soc2009/model-validation] Added custom messages to models

No tests yet and it broke queryset pickling

git-svn-id: http://code.djangoproject.com/svn/django/branches/soc2009/model-validation@11398 bcc190cf-cafb-0310-a4f2-bffc1f526a37

tests/modeltests/validation/test_messages.py

@@ -0,0 +1,8 @@
+import unittest
+
+from django.db import models
+
+class CustomMessagesTests(unittest.TestCase):
+    def test_custom_message_is_used_when_present(self):
+        pass
+