Log Message:
irssi-icb: update to 0.17

This changes the upstream to a fork of the previous one, with extra
commits bringing support for irssi 1.4. Besides fixing the build (and
that of meta-pkgs/bulk-small) this also:

* Adds a buildlink3.mk file to chat/irssi;
* And therefore can avoid extracting a copy of irssi to build;
* Leverages autoreconf to build without a release (git commit ID)
* Reduces the patches required to two.

This is inspired by FreeBSD's port of the same software (irc/irssi-icb).

Tested on NetBSD/amd64; reviewed by jperkin@.