don't show discus when previewing posts/editing drafts

themes/default/post.html

@@ -16,7 +16,7 @@ <h2>{{post.title|escape}}</h2>
     <span class="date">{{post.published|date:"d F, Y"}}</span>
   </p>
 
-  {% if config.disqus_forum %}
+  {% if config.disqus_forum and not is_admin %}
     <h3 id="comments">Comments</h3>
     <div id="disqus_thread"></div>
     {% if devel %}