Copy categories outside "mask" from "oldloc" to the new locale object.
While POSIX appears to allow the old behaviour of ignoring "oldloc",
Ted and Karl convinced me that is a bug in the spec and the Austin
group almost certainly intended to require the new behaviour.
Anyway, compatibility strongly suggests the new behaviour because
most (or maybe even all?) other systems do not ignore "oldloc",
and some software appears to depend on the copying from "oldloc"
to the new locale.

Issue analyzed and reported by Karl Williamson <public at
khwilliamson dot com> with support from the Perl 5 community.
This final diff is similar to two earlier diffs from Ted,
but handles invalid input in a mode robust way.
OK tedu@.

New POSIX xlocale implementation written from scratch.
Complete in the sense that all POSIX *locale(3) and *_l(3) functions
are included, but in OpenBSD, we of course only really care about
LC_CTYPE and we only support ASCII and UTF-8.

With important help from kettenis@, guenther@, and jca@.
Repeated testing in ports bulk builds by naddy@.
Additional testing by jca@, sebastia@, dcoppa@, and others.
OK kettenis@ dcoppa@, and guenther@ on an earlier version.
Riding guenther@'s libc/librthread major bump.

New POSIX xlocale implementation written from scratch.
Complete in the sense that all POSIX *locale(3) and *_l(3) functions
are included, but in OpenBSD, we of course only really care about
LC_CTYPE and we only support ASCII and UTF-8.

With important help from kettenis@, guenther@, and jca@.
Repeated testing in ports bulk builds by naddy@.
Additional testing by jca@, sebastia@, dcoppa@, and others.
OK kettenis@ dcoppa@, and guenther@ on an earlier version.
Riding guenther@'s libc/librthread major bump.