title: How to display customized form errors in a Ctools modal form in drupal 7
body: <p>Given a ctools modal popup in Drupal 7, and a form being displayed in it, in the mymodule_myform_validate() function, what I want to do is replace the normal drupal_message pink display of form errors at the top of the form with an error message displayed by changing the #prefix of the first field.</p>
  
  <p>What do I call to stop the modal from completing the submit and to get the field's prefix value to appear? I'm not sure whether I need to do this by having the modal execute an ajax command like ajax_before(), or whether I simply need somehow to get the form to rebuild, and what call(s) to make in this context.</p>