public function storagepurge()
 {
     if (!$this->permissions->isSuper()) {
         $this->e404();
     }
     $this->allowMethods(array('POST'));
     $purged = Zotero_S3::purgeUnusedFiles();
     header('application/xml');
     echo "<purged>{$purged}</purged>";
     exit;
 }