title: Symfony + Doctrine + MD5 issue
body: <p>I want to use the sql function MD5 in my Symfony bundle so I added the file (<a href="https://gist.github.com/Basster/2774738" rel="nofollow">https://gist.github.com/Basster/2774738</a>) in \MyCompany\MyBundle\DQL\MD5Function.</p>
  
  <p>Then I changed my config.yml file :</p>
  
  <pre><code># app/config/config.yml
  doctrine:
      orm:
          auto_generate_proxy_classes: "%kernel.debug%"
          naming_strategy: doctrine.orm.naming_strategy.underscore
          auto_mapping: true
          # Added configuration for MD5 function
          entity_managers:
              default:
                  dql:
                      string_functions:
                          MD5: MyCompany\MyBundle\DQL\MD5Function
  </code></pre>
  
  <p>But I have the following error :</p>
  
  <p>InvalidConfigurationException in ArrayNode.php line 309: Unrecognized options "naming_strategy, auto_mapping" under "doctrine.orm"</p>