Use newly added __detect_path_locale() helper to lookup _PathLocale value.
It adds boundary checking for PATH_LOCALE environment variable value and
check for super-user fallback.
Makefile:
Add lib/libc/locale to compiler's include path (for setlocale.h)
for locale related things. So, I think it could be useful for
others. It's not yet implement (or implement in different manner)
all POSIX things, but I think it's good enough for start.
POSIX conformance related updates and manpage to follow relatively soon.
