title: Prod logs in symfony 2 not using root dir
body: <p>I'm developping a symfony2 website. I'm using apache2.2.
  Everything works fine in dev environment.
  But when i want to try it on the prod environment, it goes :</p>
  
  <pre><code>Fatal error: Uncaught exception 'UnexpectedValueException' with message 'The stream or
  file "/var/www/domain/app/logs/prod.log" could not be opened:  
  fopen(/var/www/domain/app/logs/prod.log) [function.fopen]: failed to open stream: No 
  such file or directory' in /var/www/myapp/app/cache/prod/classes.php on line 4799
  </code></pre>
  
  <p>Why is it trying to write in /var/www/domain since my application is in /var/www/myapp ?
  I tried to modify the config_prod.yml to no result.
  Any idea ?</p>
  
  <p>Thanks</p>