title: django sekizai {% addtoblock %} tag is not working properly
body: <p>I'm trying to implement django sekizai app. It is duplicating the js files that i'm adding.</p>
  
  <p>base template:</p>
  
  <pre><code>{% load sekizai_tags %}
  ...
  {% render_block "my_js" %}
  </code></pre>
  
  <p>template that is using this base:</p>
  
  <pre><code>{% load sekizai_tags %}
  &lt;div id="a1" &gt;
      {% addtoblock "my_js" %}
          &lt;script type="text/javascript" src="{{ MEDIA_URL }}js/my_js.js"&gt;&lt;/script&gt;
      {% endaddtoblock %}
  &lt;/div&gt;
  {% addtoblock "my_js" %}
      &lt;script type="text/javascript" src="{{ MEDIA_URL }}js/my_js.js"&gt;&lt;/script&gt;
  {% endaddtoblock %}
  </code></pre>
  
  <p>Now here the rendered template has  rendered twice.But when I tried adding the same script within the div it wasn't duplicated. Would appreciate if someone can shed some light on this!</p>
  
  <p>Also when i try to use {% addtoblock %} in a template rendered by a template tag the script goes missing (It is neither included nor it stays in that template).</p>
  
  <p>Note: The template tags, <code>render_block</code> and <code>addtoblock</code>, are from the <a href="http://django-sekizai.readthedocs.org/en/latest/index.html" rel="noreferrer">django-sekizai</a> package.</p>