title: Two differents FOSUser in application
body: <p>I face a problem with FOSUserBundle.</p>
  
  <p>In my Symfony2 application, I want to implement two differents User.
  I have one entity User, for basic user, and one entity UserPro with more informations.</p>
  
  <p>My problem is that I want to configure my bundle with this two entities:</p>
  
  <pre><code>fos_user:
      db_driver:     orm
      firewall_name: main
      user_class:    Btp\UserBundle\Entity\User
  
  fos_userpro:
      db_driver:     orm
      firewall_name: pro
      user_class:    Btp\UserProBundle\Entity\UserPro
  </code></pre>
  
  <p>And so, use fos_user and fos_userpro as provider in my security.yml.</p>
  
  <p>I'm no sure it's be possible. I obtain an error :</p>
  
  <blockquote>
    <p>There is no extension able to load the configuration for "fos_userpro" (in /..../app/config/config.yml). Looked for namespace "fos_userpro", found "framework", "security", ...</p>
  </blockquote>
  
  <p>And when I take a look in FOSUserBundle files, I feel that fos_user is not a configuration variable and is directly written in strings.</p>
  
  <p>Thanks.</p>