Do initial port of contrib/netbsd-tests/lib/libc/locale

Do initial port of contrib/netbsd-tests/lib/libc/locale

t_io:
- Expect failures potentially related to implementation-specific knowledge of
the zh_TW.Big5 locale [*]

t_mbrtowc:
- Handle unknown locales more gracefully (do not test if the locale doesn't
exist)
- Expect failure with mbrtowc_internal dealing with Japanese locales
(potentially related to implementation detail knowledge of the ja_* locales) [*].

t_mbstowcs, t_mbtowc, t_wctomb:
- Handle unknown locales more gracefully (do not test if the locale doesn't
exist)

t_wcstod:
- Treat FreeBSD like NetBSD and Linux in the XXX: FIXME section

[*] More investigation is required to determine the root cause of the failures

Submitted by: pho
Sponsored by: EMC / Isilon Storage Division