title: Readonly method for field in Django admin interface is never called
body: <p>The Django Docs <a href="https://docs.djangoproject.com/en/dev/ref/contrib/admin/#django.contrib.admin.ModelAdmin.readonly_fields">state</a> that you can output custom HTML for readonly fields in the admin interface. This is exactly what I need, but it does not seem to work.</p>
  
  <p>In admin.py:</p>
  
  <pre><code>from django.contrib import admin
  
  class ExampleAdmin(admin.ModelAdmin):
      readonly_fields = ('myfield', )
  
      def myfield(self, instance):
          print 'This part of the code is never reached!'
          return u'&lt;b&gt;My custom html for the readonly field!&lt;/b&gt;'
  
      myfield.allow_tags = True
  
  admin.site.register(State, StateAdmin)
  </code></pre>
  
  <p>In models.py:</p>
  
  <pre><code>class State(models.Model):
      myfield = MyCustomField()
      ... etc ...
  
  class MyCustomField(models.TextField):
      def to_python(self, value):
          ... etc ...
  </code></pre>
  
  <p>The field is displayed as read-only on the admin edit page. However, the 'myfield' method that is supposed to create custom html is never called.</p>
  
  <p>Does anybody know what I'm doing wrong?</p>
  
  <p>Kind regards,</p>
  
  <p>Patrick</p>