title: Can not activate discussions on Plone Dexterity types (folderish)
body: <p>I have been working on a dexterity based plone application.
  I have created a couple of new types. This is what I did to activate comments on a specific dexterity content type named "activity_report":</p>
  
  <p><strong>In Plone Control Panel</strong></p>
  
  <p>In the <em>Discussion</em> section I enabled the following:</p>
  
  <ul>
  <li>globally enable comments</li>
  <li>enable anonymous comments</li>
  </ul>
  
  <p>In the <em>Types</em> Section 
  I chose the "Activity Report" type from the drop down and enabled the "Allow comments" option.</p>
  
  <p><strong>On the file system</strong></p>
  
  <p>In the FTI file activityreport.xml:</p>
  
  <pre><code>&lt;property name="allow_discussion"&gt;True&lt;/property&gt;
  </code></pre>
  
  <p>I have restarted the instance and even reinstalled the product, but I can not activate the comments section in the dexterity type. </p>
  
  <p>It is worth mentioning that a standard type (ex. Page) can have the discussion module activated.</p>
  
  <p>Is there something I am missing?</p>