title: Namespace problems on Symfony3 upgrade
body: <p>I'm currently trying to upgrade my Symfony2 application to Symfony3. I have a <code>SecurityController</code> that overwrites a <code>FOSUserBundle\SecurityController</code>:</p>
  
  <pre><code>namespace Acme\MyBundle\Controller;
  
  use Symfony\Component\DependencyInjection\ContainerAware;
  
  class SecurityController extends ContainerAware
  {
      // ...
  }
  </code></pre>
  
  <p>But I get a <code>ClassNotFoundException</code>:</p>
  
  <blockquote>
    <p>Attempted to load class "ContainerAware" from namespace "Symfony\Component\DependencyInjection".<br>
    Did you forget a "use" statement for another namespace?</p>
  </blockquote>
  
  <p>Are there any changes that I cannot find in the <a href="https://github.com/symfony/symfony/blob/master/UPGRADE-3.0.md" rel="nofollow">upgrade notes</a>. Can someone point me to a way to come over this?</p>