DIRInterface: added a RedirectException and a replication_toMaster call for...

DIRInterface: added a RedirectException and a replication_toMaster call for manual failover on the master-slave replication feature for the DIR

git-svn-id: https://xtreemfs.googlecode.com/svn/trunk@1200 f8528748-c2c0-11dd-ba5c-d3b7c2b3b534