Replace django.conf.urls.defaults by django.conf.urls

See <https://docs.djangoproject.com/en/1.5/ref/urls/>:
> Changed in Django 1.4: Starting with Django 1.4 functions patterns, url, include plus the handler* symbols described below live in the django.conf.urls module.
> Until Django 1.3 they were located in django.conf.urls.defaults. You still can import them from there but it will be removed in Django 1.6.