Use "NOTICE *" before registration instead of "NOTICE AUTH".

Use "NOTICE *" before registration instead of "NOTICE AUTH".

AUTH is a valid nickname so sending notices to it is probably not
a good idea. Use * as the target instead as done with numerics
when the nick is not available.

This mimics the behaviour in Charybdis, IRCD-Hybrid, InspIRCd 2.2,
Plexus 4, etc.