title: add bidirectionnal relation many to many symfony2
body: <p>I have a many to many relation between two entities in my bundle.
  I want to make this relation bidirectionnal.
  The problem is that after that I will add a request on one entity that will use the other as a parameter :</p>
  
  <p>this is in the repository of the entityA</p>
  
  <pre><code>public function findType($type,$superior)
  {
  
  $qb = $this-&gt;_em-&gt;createQueryBuilder();
  
    $qb-&gt;select('a')
       -&gt;from('xxxBundle:Profile', 'a')
       -&gt;where('a.type = :type')
       -&gt;andwhere('a.entityB = :superior')
       -&gt;setParameter('superior', $superior) 
       -&gt;setParameter('type', $type);
  
  
    $entities=$qb-&gt;getQuery()-&gt;getResult();
    return $entities;
  }
  </code></pre>
  
  <p>I get the following exception</p>
  
  <pre><code>[Semantical Error] line 0, col 84 near 'entityB = :s': Error: Invalid PathExpression. StateFieldPathExpression or SingleValuedAssociationField expected. 
  </code></pre>
  
  <p>Any ideas?????</p>