add_role.php

<?php

function drupal_commons_add_role($name) {
  module_load_include('inc', 'user', 'user.admin');
  $form_state = array();
  $form_state['values']['name'] = $name;
  $form_state['values']['op'] = "Add role";
  drupal_execute('user_admin_role', $form_state);
}