title: AttributeError: 'property' object has no attribute 'admin_order_field'
body: <p>I want to be able to define a property in a Model that can also be displayed AND sort using admin_order_field in the 'list_display' Admin property. Below is the code for a property that I wanted to define (and be sortable in the django admin interface)</p>
  
  <pre><code>  @property
    def restaurant_name(self):
      return str(self.restaurant)
    restaurant_name.admin_order_field = 'restaurant__name'
  </code></pre>
  
  <p>However, I get the following error message:</p>
  
  <pre><code>AttributeError: 'property' object has no attribute 'admin_order_field'
  </code></pre>
  
  <p>When I get rid of the @property decorator, it works fine, but then I have to call restaurant_name() on model instances, instead of restaurant_name, which provides inconsistent style in how I access different properties of the model (which are actually defined as Python properties). How do I specify a Python property as sortable in the admin?</p>