For quite a while now, the only update server for SpamAssassin hasn't
had a valid DNS entry. People have asked about it on the mailing list
as far back as August, but literally nobody has replied to any of those
posts, and no commits or wiki updates have been made regarding this,
making it reasonably appear that nobody on the SpamAssassin team has
noticed or cares that SpamAssassin no longer updates.

For now, just add a patch that turns sa-update(1) into a no-op.

While here, add a couple simple Makefile tweaks and bump PORTREVISION.