title: Django Admin + Filter Horizontal?
body: <p>I've added <a href="http://docs.djangoproject.com/en/dev/ref/contrib/admin/#django.contrib.admin.ModelAdmin.filter_horizontal" rel="noreferrer">filter horizontal</a></p>
  
  <pre><code>filter_horizontal = ('blocked_email_notifications',)
  </code></pre>
  
  <p>To my <code>ModelAdmin</code>, but it's still rendering it as a multiple select widget, rather than the nifty javascript enhanced version. How come? Do I need to add something else?</p>
  
  <p>The user model has it defined as</p>
  
  <pre><code>blocked_email_notifications = ManyToManyField('EmailTemplate', blank=True)
  </code></pre>
  
  <p>And the form has it defined as</p>
  
  <pre><code>blocked_email_notifications = ModelMultipleChoiceField(queryset=EmailTemplate.objects.order_by('key'), required=False)
  </code></pre>