try to use timestamped version if exist locally

git-svn-id: https://svn.apache.org/repos/asf/archiva/trunk@1475709 13f79535-47bb-0310-9956-ffa450edef68
use StringBuilder and add a debug log

git-svn-id: https://svn.apache.org/repos/asf/archiva/trunk@1475710 13f79535-47bb-0310-9956-ffa450edef68