title: Trouble searching User model using django-ajax-selects
body: <p>I´m using <a href="http://code.google.com/p/django-ajax-selects/" rel="nofollow">django-ajax-selects</a> in my project, and I can´t make it to work with <em>django.contrib.auth.models.User</em>. All I want to do is search the <em>username</em> field and I don´t know how to put it in my settings.py. What I have now is:</p>
  
  <pre><code>AJAX_LOOKUP_CHANNELS = {
      'to' : dict(model='django.contrib.auth.User', search_field='username'),
  }
  </code></pre>
  
  <p>If I search one of my models, like this</p>
  
  <pre><code>AJAX_LOOKUP_CHANNELS = {
      'to' : dict(model='books.Book', search_field='title'),
  }
  </code></pre>
  
  <p>Everything works fine, so I think I just need to know what to put in the model parameter.</p>