title: zf2 change error code returned by Callback validator
body: <p>I successfully use the <a href="http://framework.zend.com/manual/2.3/en/modules/zend.validator.callback.html" rel="nofollow">ZF2 <code>Callback</code> validator</a> but I have a problem with the code that it returns. Here the config that use:</p>
  
  <pre><code>'validators'=&gt;array(
      array(
          'name' =&gt; 'Callback',
          'options' =&gt; array(
              'messages'=&gt;array(
                  Callback::INVALID_VALUE =&gt; 'Error',
              ),
              'callback' =&gt; function ($value,$context=array()) {
                  if(empty($value) &amp;&amp; empty($context['company'])){
                      $isValid = false;
                  }else{
                      $isValid = true;
                  }
                  return $isValid;
              },
          )
      )
  ),
  </code></pre>
  
  <p>The problem is in the error code which returns no message</p>
  
  <p>It returns <code>callbackValue</code> which is the value of the constant <code>INVALID_VALUE</code> of the <code>Callback</code> validation class</p>
  
  <p>Is there a way to change this value through the options?</p>
  
  <p>I would like to avoid writing a custom class for each item that I have to validate.</p>