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.

Introduction
============

This module checks the IP address of newly registered users against a
DNS block list. If a positive match is found, it gets logged.

Configuration
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  Option              Type     Default
  ------------------- -------- ------------
  registration\_rbl   string   *Required*