Fixed #15597: When formatting the debug page for inclusion in an e-mail, suppress the note about "seeing this" because DEBUG is True.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@15802 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/views/debug.py

@@ -756,14 +756,15 @@ Exception Value: {{ exception_value|force_escape }}
   </table>
 
 </div>
-
-<div id="explanation">
+{% if not is_email %}
+  <div id="explanation">
     <p>
       You're seeing this error because you have <code>DEBUG = True</code> in your
       Django settings file. Change that to <code>False</code>, and Django will
       display a standard 500 page.
     </p>
-</div>
+  </div>
+{% endif %}
 </body>
 </html>
 """