irssi: add patch for buf.pl update as it is shipped with irssi.

previously it would create a world readable file containing chat
logs when /upgrade was used.

while a security fix, you have to jump through many hoops to be
affected by it - we don't enable perl scripts by default, we
don't run that perl script by default, and you'd have to know that
/upgrade exists in the first place, and run on a system where world
readability of files is a concern.

still, grab upstream update, bump PKGREVISION.

(maya)