title: django admin list_filter "or" condition
body: <p>sorry if this question has been answered before, but I did a lot of googling without success.</p>
  
  <p>I know how to create custom <code>list_filter</code>s in admin views (e.g. subclassing <code>SimpleFilter</code>). </p>
  
  <p>What I really would like, is a way (on the admin list view) to "check" different filters that combines them in a OR formula.</p>
  
  <p>As an example, suppose you have:</p>
  
  <pre><code># models.py
  class Foo(models.Model):
      foobar = ...
      foofie = ...
  ...
  
  # admin.py
  class FooAdmin(admin.ModelAdmin):
      list_filter = ( "foobar", "foofie" )
  ...
  </code></pre>
  
  <p>In the admin list view generated by <code>FooAdmin</code> I can choose to filter records either by <code>foobar</code> or by <code>foofie</code>. Is there a way to filter them by the formula: <code>foobar = X OR foofie = Y</code>, where <code>X</code> and <code>Y</code> are two values that <code>foobar</code> and <code>foofie</code> can assume?</p>
  
  <p>Is it even possible?</p>
  
  <p>I know not everything is possible in the django admin views, but it seems a very common request, I wonder if I missed to understand or read something. </p>
  
  <p>Also third party apps allowing it are welcome. Thanks :)</p>