Jan Mayen in wrong zone

[Paul Eggert]

> From: Jonas Melian [mailto:jonas at mailup.net] 
> Sent: Friday, November 09, 2007 6:08
>
> Jan Mayen has been placed ('zone.tab' file) in the Atlantic zone
> but it's too in the Arctic [1] as Svalbard.

Good catch.  Come to think of it, this suggests that we should remove
Atlantic/Jan_Mayen, since there's no particular reason to have
duplicate entries Arctic/Longyearbyen and Arctic/Jan_Mayen: those
entries would have the same time zone history, country code, and
continent.  (By "remove" I really mean "move to the 'backward' file",
of course; we want to continue to support those dozen or so people who
are stuck on Jan Mayen right now!)