title: django join querysets from multiple tables
body: <p>If I have queries on multiple tables like:</p>
  
  <pre><code>d = Relations.objects.filter(follow = request.user).filter(date_follow__lt = last_checked)
  r = Reply.objects.filter(reply_to = request.user).filter(date_reply__lt = last_checked)
  article = New.objects.filter(created_by = request.user)
  vote = Vote.objects.filter(voted = article).filter(date__lt = last_checked)
  </code></pre>
  
  <p>and I want to display the results from all of them ordered by date (I mean not listing all the replies, then all the votes, etc ).
  Somehow, I want to 'join all these results', in a single queryset.
  Is there possible?</p>