title: Doctrine2 findBy relationship object triggers string conversion error
body: <p>Say I have two entities in Doctrine2 that are related to each other, Models\User and Models\Comment. If I do this in Doctrine 2.0.0...</p>
  <pre><code>&lt;?php
  // $em instanceof EntityManager, $user instanceof Models\User
  $comments = $em-&gt;getRepository('Models\Comment')
      -&gt;findBy(array('user' =&gt; $user, 'public' =&gt; true));
  </code></pre>
  <p>...I get a PHP error:</p>
  <blockquote>
  <p>Severity: Notice</p>
  <p>Message: Object of class Models\User to string conversion</p>
  <p>Filename: DBAL/Connection.php</p>
  <p>Line Number: 574</p>
  </blockquote>
  <p>This shouldn't happen, right? If I use the QueryBuilder and setParameter('user', $user) it works as expected.</p>