frontend.settings: Add MessageMiddleware among the middleware classes

So we can effectively show up popup messages in the Django
admin view. As this class was introduced in 1.2, this change
should also allow to use Django 1.3 as a supported dep.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>

frontend/settings.py

@@ -92,6 +92,7 @@ def _get_config(config_key, default=None):
 MIDDLEWARE_CLASSES = (
     'django.middleware.common.CommonMiddleware',
     'django.contrib.sessions.middleware.SessionMiddleware',
+    'django.contrib.messages.middleware.MessageMiddleware',
     'frontend.apache_auth.ApacheAuthMiddleware',
     'django.contrib.auth.middleware.AuthenticationMiddleware',
     'django.middleware.doc.XViewMiddleware',