[tz] McMurdo/South Pole

[Paul Eggert]

McMurdo is a special case of a more general problem, which
is the representation of locations while uninhabited.
*Every* location in the tz database was uninhabited at
*some* point, and the tz database does not attempt to
systematically record the details of when a location
was inhabited and when it wasn't, as that's outside the
scope (and the values are typically unknown anyway).
In practice I've used "zzz" entries for uninhabited
locations only when the database format *forced* a value.
When it doesn't force a value I haven't worried about it,
and I'd rather not start worrying about it now.

There's an amusing instance of the opposite problem in
Pacific/Johnston, which was inhabited when we created
the tz database but became uninhabited in 2004.
Its entry cheerily says "We're just like Honolulu!",
and really, that's OK: worrying about the discrepancy
would be more trouble for everybody than it's worth.