Emulate POSIX locale setting on Windows

Emulate POSIX locale setting on Windows

Locale initialization and setting on Windows haven't been as
described in perllocale for setting locales to "".  This is because that
tells Windows to use the system default locale, as set through the
Control Panel, but on POSIX systems, it means to look at various
environment variables.

This commit creates a wrapper for setlocale, used only on Windows, that
looks for the appropriate environment variables when called with a ""
input locale.  If none are found, it continues to use the system default
locale.