title: Symfony: Error with File Constraint
body: <pre><code>-&gt;add('shots','file', array(
      'multiple' =&gt; true,
      **'constraints' =&gt; array(
          new Constraints\Image(array(
              'maxSize' =&gt; '10M',
              'allowSquare' =&gt; false,
              'allowPortrait' =&gt; false,
              'minRatio' =&gt; 1.43,
              'maxRatio' =&gt; 2.4
          )),
      )**
  ))
  </code></pre>
  
  <p>This is part of a symfony form with intgrated form validator. But I get an error I dont understand:</p>
  
  <pre><code>UnexpectedTypeException: Expected argument of type "string", "array" given
  </code></pre>
  
  <p>Without the <strong>marked part</strong> everthing does work. I checked the reference of the form constraints, but I didn't get the solution ...</p>