title: register_theme_directory in plugin not working
body: <p>I'm trying to register a theme folder within my plugin directory so that I can have "standard" themes for pages and stuff. Users can overwrite these in their own theme folder if they wish, but at least there is a "skeleton" for users.</p>
  
  <p>I have found out about the function <code>register_theme_directory()</code> but it doesn't seem to be working as expected.</p>
  
  <p>Here is my code:</p>
  
  <pre><code>add_filter('init', 'test_templates_dir');
  function test_templates_dir(){
      $plugindir = dirname( __FILE__ );
      register_theme_directory($plugindir."/themefiles");
  }
  </code></pre>
  
  <p>Inside my <code>$plugindir."/themefiles"</code> directory I have a file called <code>tpl-directory.php</code> and inside that template file I have this:</p>
  
  <pre><code>&lt;?php
  /*
   *Template name: Directory template
   */
  ?&gt;
  </code></pre>
  
  <p>This isn't coming up in the list of available templates when I'm "adding new" pages however.</p>
  
  <p>What am I doing wrong? Does anyone know? Or does anyone know a better way to do what I'm trying to achieve? I have read that there are no filters or hooks in order to "add template files manually" (although I would be pretty happy with that if I can do it that way!).</p>
  
  <p>Many thanks!</p>