Require xmlseclibs in Validator class.

git-svn-id: https://simplesamlphp.googlecode.com/svn/trunk@589 44740490-163a-0410-bde0-09ae8108e29a

lib/SimpleSAML/XML/Validator.php

 <?php
 
+require_once((isset($SIMPLESAML_INCPREFIX)?$SIMPLESAML_INCPREFIX:'') . 'xmlseclibs.php');
+
 /**
  * This class implements helper functions for XML validation.
  *