title: data-add-back-btn does not show a back button
body: <p>I have a simple jQuery mobile site with three pages in it.
  In every page's div I've added</p>
  
  <pre><code>data-add-back-btn="true"
  </code></pre>
  
  <p>Still on none of the pages (not even on the sub-pages) a back button appears.
  Is there some trick to this?</p>