Really update to version 2.2.1

Just updating PORTVERSION won't achieve anything if you don't also
make the corresponding change to GH_TAGNAME. To avoid this sort of
embarrassment in future, drop PORTVERSION and GH_TAGNAME for the main
distfile in favour of DISTVERSION and DISTVERSIONPREFIX.

Reorder some items in the Makefile to mollify portlint.

Reported by: mat