Fixed Python 2.3 problem I introduced all the way back in [6852]. :-(

git-svn-id: http://code.djangoproject.com/svn/django/trunk@7000 bcc190cf-cafb-0310-a4f2-bffc1f526a37

tests/regressiontests/middleware/tests.py

@@ -66,7 +66,7 @@ class CommonMiddlewareTest(TestCase):
         try:
             CommonMiddleware().process_request(request)
         except RuntimeError, e:
-            self.assertTrue('end in a slash' in str(e))
+            self.failUnless('end in a slash' in str(e))
         settings.DEBUG = False
 
     def test_append_slash_disabled(self):