mod_pubsub_serverinfo: Detect existence of pub/sub node Instead of blindly trying to create the pub/sub node to publish items to, a service discovery query is performed to check if node creation is required. Added various bits of warn and debug logging, to give a user better feedback if and why something is failing.

-- this module is deprecated, log an error and load the superseding modules instead
module:depends"smacks"
module:depends"nooffline_noerror"

module:log("error", "mod_smacks_noerror is deprecated! Just use mod_smacks and load mod_nooffline_noerror if you explicitly disabled offline storage (mod_offline)");