Pdns registration update

this code allows a nodes IP address (A and PTR) records to be created/updated based on the following conditions:

* If an IP exists already, but hostname does not, do not overwrite, add to events.
* If the Hostname exists, but the IP is wrong, update the IP address, notify of the former IP and the new IP and add to events.
* If neither Hostname nor IP exist, simply add the DNS entry.