Mine

function messages_get() {
  $messages = $_SESSION['messages'];
  $complete = array();
  foreach($messages as $type => $message) {
    foreach($message as $m) {
      $complete[$type][$m] = $m;
    }
  } 
  return $complete;
}
function message_set($messages) {
  unset($_SESSION['messages']);
  foreach($messages as $type => $message) {
    foreach($message as $m) {
      $_SESSION[$type][] = $m;
    }
  }
}