Fixed #17895 -- Made override_settings send the setting_changed signal both when a setting is overridden and when it's restored.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@17708 bcc190cf-cafb-0310-a4f2-bffc1f526a37

tests/regressiontests/settings_tests/tests.py

@@ -132,6 +132,7 @@ class SettingsTests(TestCase):
         self.assertRaises(AttributeError, getattr, settings, 'TEST')
         with self.settings(TEST='override'):
             self.assertEqual(testvalue, 'override')
+        self.assertEqual(testvalue, None)
 
     @override_settings(TEST='override')
     def test_signal_callback_decorator(self):