title: Symfony 2 form extra fields
body: <p>Im changing some fields via AJAX and when im trying to save a form i recive a error that <code>Extra fields are not allowed</code>.</p>
  
  <p>How to change that validator property like <code>validatorPass()</code> in sf1.4 ?<br>
  Or its possible change to form to accept extra fields ?</p>
  
  <p>Im using SonataAdminBundle to create forms.</p>