Returns names of available search modules.
array An array of the names of enabled modules that call hook_search_info sorted into alphabetical order.
protected function getModuleOptions() {
$search_info = search_get_info(TRUE);
$names = system_get_module_info('name');
$names = array_intersect_key($names, $search_info);
asort($names, SORT_STRING);
return $names;
}