title: Symfony translation inside validation won't work
body: <p>If I try to use translations inside validation like described here
  <a href="http://inchoo.net/tools-frameworks/symfony2-translating-validator-messages/" rel="nofollow">http://inchoo.net/tools-frameworks/symfony2-translating-validator-messages/</a></p>
  
  <p>I get always </p>
  
  <pre><code>not.blank.username
  </code></pre>
  
  <p>as output on Error. It seems like symfony didn't find the message-translation. I placed all my translationfiles inside app/ressources/translations and they are named as</p>
  
  <pre><code>messages.de.yml
  ....
  </code></pre>
  
  <p>What am I doing wrong? Do I have to place the translationfiles insde each Bundle? </p>
  
  <p>Kind regards</p>
  
  <p>EDIT: Problem ist clear and fixed, but when I  try to use "MinLength" I get an strange error:</p>
  
  <pre><code>Attempted to load class "MinLength" from namespace 
  "Symfony\Component\Validator\Constraints" in /var/www/symfony/webprojekt/vendor/symfony/symfony/src/Symfony/Component/Validator/Mapping/Loader/AbstractLoader.php line 64. 
  Do you need to "use" it from another namespace? 
  </code></pre>
  
  <p>I already included </p>
  
  <pre><code>use Symfony\Component\Validator\Mapping\ClassMetadata;
  use Symfony\Component\Validator\Constraints\NotBlank;
  use Symfony\Component\Validator\Constraints\Email;
  use Symfony\Component\Validator\Constraints\MinLength;
  use Symfony\Component\Validator\Constraints\MaxLength;
  </code></pre>
  
  <p>AM I missing something?</p>