Ajax callback for 'settings' but with setting overrides.
function ajax_forms_test_advanced_commands_settings_with_merging_callback($form, $form_state) {
drupal_add_js(array(
'ajax_forms_test' => array(
'foo' => 42,
),
), 'setting');
drupal_add_js(array(
'ajax_forms_test' => array(
'foo' => 9001,
),
), 'setting');
$response = new AjaxResponse();
return $response;
}