Fix the problem that PKGVERSION for 173.14.xx legacy driver went backwards
when it was updated to .35 on the 12th. That moment, it kept PORTREVISION
1 from the master port. When the master port was updated and PORTREVISION
removed on the 22nd, PKGVERSION of nvidia-driver-173 went backwards as its
PORTREVISION dropped from 1 to 0. While I am at it, provide a comments in
all makefiles that keeping PORTREVISION setting (even when it is seemingly
zero) is important.
Reported by: erwin