[XrdCl] Make client plug-ins configurable
[XrdCl] Move the ttl expiration logic to socket timeout handler
[XrdCl] Bump the timestamp of last activity only upon receiving a non-timeout event
Adjusting the listing behavior strictly following the protocol docs
Merge branch 'master' of https://github.com/ffurano/xrootd-fbx3 into ffurano-master