title: Symfony2: cache busting and versioning assets with Assetic
body: <p>Who knows how to add versions to assets that was loaded inside Assetic blocks globally ?</p>
  
  <p>Added to my config.yml</p>
  
  <pre><code>templating:
      engines: ['twig']
      assets_version: v2
  </code></pre>
  
  <p>it works for regular assets, but doesn't for asset_url inside stylesheets and javascripts assetic blocks 
  Am I doing somethg wrong or it's some kind of a bug ?</p>
  
  <p>small upd.
  it doesn't work without assets_version_format</p>