p5-ack renamed ack, no entry in UPDATING

[Vick Khera]

The ports/UPDATING file has no mention of textproc/p5-ack being renamed to
textproc/ack.  There should be some note about this, as well as suggestion
to use portupgrade/portmaster/pkg to replace the installed version. I did
this:

portmaster -o textproc/ack p5-ack-1.96_1

Somehow I ended up with both ports installed after a recent run of
portupgrade -a.