title: Filtering a Django queryset with a limited subquery
body: <p>I'm trying to get a queryset, and limit based on a limited set of subqueries.
  It seems to be returning only a limited set of the first query.</p>
  
  <p><code>photos = Photo.objects.filter(event=Event.objects.all().order_by('date')[:5]).order_by('event')</code></p>
  
  <p>I'm trying to get all photo in the five most recent events.</p>