title: Django REST framework - SearchFilter not filtering
body: <p>I am using <code>Django 1.10</code> and <code>django-rest-framework 3.5.3</code>.
  I would like to have a generic search query: search for a value on many fields.
  I Found the <a href="http://www.django-rest-framework.org/api-guide/filtering/#searchfilter" rel="nofollow noreferrer">SearchFilter</a> on the Docs.</p>
  
  <p>I tried to add the filter backend to the ViewSet, but it seems not to be working. Any search query response with all the objects.</p>
  
  <p>ViewSet:</p>
  
  <pre><code>from rest_framework import filters
  
  class UserViewSet(viewsets.ModelViewSet):
      queryset = User.objects.all().order_by('-date_joined')
      serializer_class = UserSerializer
      filter_backends = (filters.SearchFilter,)
      filter_fields = ['username', 'email', 'is_staff', 'groups']
  </code></pre>
  
  <p>Query url:</p>
  
  <pre><code>http://localhost:8000/users/?search=something
  </code></pre>
  
  <p>In addition, at the docs they show that a new button "Filter" added to the django rest web page. It does not in my case.</p>