Tweaked some `AutoField` tests to not raise wanings in Python>=2.6, where `BaseException.message` has been deprecated.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@17045 bcc190cf-cafb-0310-a4f2-bffc1f526a37

tests/modeltests/validation/models.py

@@ -102,4 +102,4 @@ try:
         auto2 = models.AutoField(primary_key=True)
 except AssertionError, assertion_error:
     pass # Fail silently
-assert assertion_error.message == u"A model can't have more than one AutoField."
+assert str(assertion_error) == u"A model can't have more than one AutoField."

tests/modeltests/validation/test_error_messages.py

@@ -17,7 +17,7 @@ class ValidationMessagesTest(TestCase):
         try:
             models.AutoField(primary_key=False)
         except AssertionError, e:
-            self.assertEqual(e.message, u"AutoFields must have primary_key=True.")
+            self.assertEqual(str(e), "AutoFields must have primary_key=True.")
 
     def test_integer_field_raises_error_message(self):
         f = models.IntegerField()