use SimpleXMLElement class for creating XML
use \VuFind\Date\Converter for working with dates
use default patron id for getHolding when user is not logged in
description of AVA tag used in getStatusesX
unused variable removed
cleanup in getHolding method (avoid use of xpath for simple cases)
Aleph driver: fix for PHP 5.4
AlephRestfulException extends ILSException
log failed DLF requests
do not return empty array on failed request in getHolding
Style fixes.