title: Symfony, querybuilder, use extension from pgsql
body: <p>I'm using <code>createQueryBuilder</code> with <code>Symfony</code> and <code>PGSQL</code>.</p>
  
  <p>I installed the extension unaccent from PGSQL in my database with : </p>
  
  <pre><code>CREATE EXTENSION unaccent;
  </code></pre>
  
  <p>But when i try a query like : </p>
  
  <pre><code>                    $qb = $this-&gt;_em-&gt;createQueryBuilder();
                      $qb-&gt;select(array('a'))
                      -&gt;from('ProjectBundle:Account', 'a')
                      -&gt;where('unaccent(a.firstname) LIKE unaccent(?1) OR unaccent(a.lastname) LIKE unaccent(?1)')
                      -&gt;setParameters(array(1 =&gt; '%'.$search.'%'))
                      -&gt;setMaxResults(5);
              return $qb-&gt;getQuery()-&gt;getResult();
  </code></pre>
  
  <p>I have this error : <code>Error: Expected known function, got unaccent</code></p>
  
  <p>How can i use this extension with Symfony and Doctrine ? </p>