Added RBL lookups on connection via DroneDL.

RBL lookups are turned on by dedault and highly recommended all irc admins leave it in place. This will block known spambots from invading the Synchronet IRC network. If you want to add this to an older version of the ircd, take the checkip function from core.js along with the section between RBL comments and added them to the older version. Thanks to Keyop for finding DroneDL.