title: Symfony2 add reCaptcha field to registration form
body: <p>I'm trying to add EWZRecaptcha to my registration form.
  My registration form builder looks something like this:</p>
  
  <pre><code>public function buildForm(FormBuilder $builder, array $options)
  {
      $builder-&gt;add('username',  'text')
              -&gt;add('password')
              -&gt;add('recaptcha', 'ewz_recaptcha', array('property_path' =&gt; false));
  }
  
  public function getDefaultOptions(array $options)
  {
      return array(
              'data_class' =&gt; 'Acme\MyBundle\Entity\User',
      );
  }
  </code></pre>
  
  <p>Now, how can I add the Recaptcha Constraint to the captcha field? I tried to add this to validation.yml:</p>
  
  <pre><code>namespaces:
    RecaptchaBundle: EWZ\Bundle\RecaptchaBundle\Validator\Constraints\
  
  Acme\MyBundle\Entity\User:
    ...
    recaptcha:
      - "RecaptchaBundle:True": ~
  </code></pre>
  
  <p>But I get <code>Property recaptcha does not exists in class Acme\MyBundle\Entity\User</code> error.</p>
  
  <p>If I remove <code>array('property_path' =&gt; false)</code> from the recaptcha field's options, I get the error:</p>
  
  <pre><code>Neither property "recaptcha" nor method "getRecaptcha()" nor method "isRecaptcha()"
  exists in class "Acme\MyBundle\Entity\User"
  </code></pre>
  
  <p>Any idea how to solve it? :)</p>