Remember .include "foo.mk" is looked for (first) in the directory that
contains the makefile being processed (like in C), so remove all the
${.PARSEDIR} and ../ sequences that just cause grief.
and to support the "inet6" option instead.
Remaining usage of USE_INET6 was solely for the benefit of the scripts
that generate the README.html files. Replace:
BUILD_DEFS+= USE_INET6
with
BUILD_DEFS+= IPV6_READY
and teach the README-generation tools to look for that instead.
This nukes USE_INET6 from pkgsrc proper. We leave a tiny bit of code
to continue to support USE_INET6 for pkgsrc-wip until it has been nuked
from there as well.