title: renderFile do not load custom Twig extensions
body: <p>I'm trying to create my own Generator, using SensioGeneratorBundle as a core. But there is a problem with custom Twig extensions loading.
  If I use</p>
  
  <p><code>return $this-&gt;container-&gt;get('templating')-&gt;renderResponse('Acme:Generator/Work:edit.html.twig', array());</code></p>
  
  <p>extension is working, but if I use</p>
  
  <pre><code>return $this-&gt;renderFile('edit.html.twig', array('entity' =&gt; $entity));
  </code></pre>
  
  <p>where</p>
  
  <pre><code>protected function renderFile($template, $parameters)
  {
      $twig = new \Twig_Environment(new \Twig_Loader_Filesystem($this-&gt;skeletonDirs), array(
          'debug'            =&gt; true,
          'autoReload'       =&gt; true,
          'cache'            =&gt; false,
          'strict_variables' =&gt; true,
          'autoescape'       =&gt; true,
      ));
  
      return $twig-&gt;render($template, $parameters);
  }
  </code></pre>
  
  <p>Only core Twig extensions are loaded. And I get an error </p>
  
  <blockquote>
    <p>The filter "price" does not exist in edit.html.twig at line 9</p>
  </blockquote>
  
  <p>Any ideas?</p>