title: Python Django Admin Clean() Method not overiding values
body: <p>Maybe I am missing something here, but according to the django docs, I should be able to overide values sent from an admin form from within the clean() method.
  From django docs</p>
  
  <pre><code>def clean(self):
      from django.core.exceptions import ValidationError
      # Don't allow draft entries to have a pub_date.
      if self.status == 'draft' and self.pub_date is not None:
          raise ValidationError('Draft entries may not have a publication date.')
      # Set the pub_date for published items if it hasn't been set already.
      if self.status == 'published' and self.pub_date is None:
          self.pub_date = datetime.date.today()
  </code></pre>
  
  <p>I have stripped down my code and am just trying a basic example here from within the admin</p>
  
  <p>Models.py</p>
  
  <pre><code>class Test(models.Model):
  name = models.CharField(max_length=255,)
  
  def clean(self):
      self.name = 'Robin Hood'
      return self
  </code></pre>
  
  <p>So when I try and add a new Test record, if I leave the name field empty, it should grab the value from the clean method and save.</p>
  
  <p>What happens though, is that the form doesnt validate, and the field remains empty.</p>
  
  <p>Am I missing something blantantly obvious here?</p>