title: Infinite recursion while extending the admin's app change_form template
body: <p>I have the following template in <code>template/admin/change_form.html</code>:  </p>
  
  <pre><code>{% extends "admin/change_form.html" %}
  {% block extrahead %}
    {% include "dojango/base.html" %}
    {% block dojango_content %}
    {% endblock %}
  {% endblock %}
  </code></pre>
  
  <p>However for some reason it throws a </p>
  
  <pre><code>TemplatesyntaxError: TemplateSyntaxError at /admin/cms/post/add/
  Caught RuntimeError while rendering: maximum recursion depth exceeded while calling a Python object
  </code></pre>