title: models.CharField max_length less in django admin page
body: <p>I have a model class with following field</p>
  
  <pre><code>aliases = models.CharField(max_length=500,default=None,blank=True,null=True)
  </code></pre>
  
  <p>Now, when I try to edit this on Django admin page its maxlength is <code>20</code></p>
  
  <pre><code>&lt;input class="vTextField" id="id_alias" maxlength="20" name="alias" type="text" value="ABCD,AAA"&gt;
  </code></pre>
  
  <p>I can't edit it.</p>