/**

  * Invokes a hook in all enabled modules that implement it.

  *

  * All arguments are passed by value. Use drupal_alter() if you need to pass

  * arguments by reference.

  *

  * @param $hook

  *   The name of the hook to invoke.

  * @param ...

  *   Arguments to pass to the hook.

  *

  * @return

  *   An array of return values of the hook implementations. If modules return

  *   arrays from their implementations, those are merged into one array.

  *

  * @see drupal_alter()

  */

 function module_invoke_all($hook) {

   $args = func_get_args();

   // Remove $hook from the arguments.

   unset($args[0]);

   $return = array();

   foreach (module_implements($hook) as $module) {

     $function = $module . '_' . $hook;

     if (function_exists($function)) {

       $result = call_user_func_array($function, $args);

       if (isset($result) && is_array($result)) {

         $return = array_merge_recursive($return, $result);

       }

       elseif (isset($result)) {

         $return[] = $result;

       }

     }

   }

   return $return;

 }