title: How to extend/overwrite symfony2 form_row function
body: <p>I would like to use <code>form_row(form.myfield)</code> in my twig template to render the whole row (label, error, widget) of a form field.</p>
  
  <p>But I would like to overwrite the <code>form_widget()</code> function to give out some help message.</p>
  
  <p>My question now is: How to extend/overwrite the <code>form_row()</code> function to add an attribute with my help message, that is transfered to the <code>form_widget()</code> function?</p>
  
  <p>What i would like to use:</p>
  
  <pre><code>{ form_row(form.firstname, { 'attr': {'helpmsg': 'I am your help buddy'} }
  </code></pre>