title: Class meta got invalid attributes
body: <p>Please help to fix this Meta class value as I gave up after detailed research.
  I am getting back error while trying to handle template urls with "get_absolute_url" as it responds with following error.</p>
  
  <blockquote>
    <p>TypeError: 'class Meta' got invalid attribute(s): sale_price,get_absolute_url.</p>
  </blockquote>
  
  <p>Below is my code. </p>
  
  <pre><code>class Meta:
          db_table = 'products'
          ordering = ['-created_at']
  
          def __unicode__(self):
              return self.name
  
          @models.permalink
          def get_absolute_url(self):
              return ('catalog_product', (), {'product_slug': self.slug})
  
          def sale_price(self):
              if self.old_price &gt; self.price:
                  return self.price
              else:
                  return None
  </code></pre>
  
  <p>Thanks. </p>