For a Mac user in Australia, for example, the out-of-the-box configuration is
that the preferred language is generic English ("en").  Their formats locale
should be Australia ("en_AU").  Detect that case and don't override
LC_MESSAGES.

This enables it to be auto-updated by make_makefiles.

Listview receives notifications not only from built-in header control,
but also from custom or subclassed application controls, there is no
need to assert(0) on application input, printing a FIXME is the maximum
we can do on an unknown input.