/**
 * Get the list of files that already being upraded
 *
 * @return array
 * @access private
 */
function ossn_get_upgraded_files()
{
    $settings = new OssnSite();
    $upgrades = $settings->getSettings('upgrades');
    $upgrades = json_decode($upgrades);
    if (!is_array($upgrades) || empty($upgrades)) {
        $upgrades = array();
    }
    return $upgrades;
}