title: Assetic generating links but no files
body: <p>I'm trying to use assetic in symfony2 to manage my css. 
  The links are generated fine. However, no files are generated.</p>
  
  <p>Here's my configuration:</p>
  
  <p><strong>Layout.html.twig</strong></p>
  
  <pre><code>    {% stylesheets
        '@FooBundle/Resources/public/css/main.css'
        filter='cssrewrite'
      %}
      &lt;link rel="stylesheet" href="{{ asset_url }}" /&gt;
      {% endstylesheets %}
  </code></pre>
  
  <p><strong>Config.yml</strong></p>
  
  <pre><code>assetic:
  debug:          %kernel.debug%
  use_controller: false
  bundles:        [ FooBundle ]
  filters:
      cssrewrite: ~
  </code></pre>
  
  <p><strong>Config_dev.yml</strong></p>
  
  <pre><code>assetic:
  use_controller: true
  </code></pre>
  
  <p>Assetic generates te link <code>foo.foo/app_dev.php/css/957d3aa_main_1.css</code>. However, the file isn't there (or anywhere else). I've tried playing around with permissions and looking in the (nginx) logs, but nothing so far.</p>
  
  <p>All help would be greatly appreciated.</p>