title: Assetic unable to find file
body: <p>I am trying to link a css file (that lives in a bundle) inside a twig template :</p>
  
  <pre><code>{% stylesheets 
      '@AcmeFooBundle/Resources/public/css/bootstrap.min.css' 
  %}
      &lt;link href="{{ asset_url }}" rel="stylesheet"/&gt;
  {% endstylesheets %}
  </code></pre>
  
  <p>The first error message I get is: </p>
  
  <p><em>You must add AcmeFooBundle to the assetic.bundle config...</em></p>
  
  <p>This is the config :</p>
  
  <pre><code># Assetic Configuration
  assetic:
      debug:          %kernel.debug%
      use_controller: false
      bundles:        []
      #java: /usr/bin/java
      filters:
          cssrewrite: ~
          #closure:
          #    jar: %kernel.root_dir%/Resources/java/compiler.jar
          #yui_css:
          #    jar: %kernel.root_dir%/Resources/java/yuicompressor-2.4.7.jar
  </code></pre>
  
  <p>Then I try to add AcmeFooBundle in the <strong>bundles</strong> directive but then I get an error:</p>
  
  <p><em>Unable to find file....</em></p>
  
  <p>I can't understand what I am doing wrong here... </p>
  
  <p>Dumping the default configs of the assetic configuration in the console (using <strong>php app/console config:dump-reference assetic</strong> ) I can see AcmeFooBundle bundle listed in the <strong>bundles</strong> directive...</p>