src/irc.c:

src/irc.c:
	Upon connection to the IRC server, initialise our negative cache
	(if negative caching is enabled).

	When a user connection is detected, search for their IP in our
	negative cache (if negative caching is enabled).  If it is present,
	say so in the logfile and don't bother to scan them.

	Note that negative caching is only implemented for IPv4 at the
	moment -- shouldn't be hard to extend it to IPv6 though.