* .gitignore: Add 'leapseconds'.

This follows up on the previous change, since 'leapseconds'
is now generated automatically.
Revert most of the recent zone.tab changes.

* iso3166.tab, zone.tab: Make it clear that country codes aren't
necessarily for countries.  Thanks to Derick Rethans for spotting this.
* zone.tab (Antarctica/McMurdo, Europe/Mariehamn, Europe/Sarajevo)
(America/St_Barthelemy, America/Kralendijk, Europe/Busingen)
(Europe/Guernsey, Europe/Zagreb, Europe/Isle_of_Man, Europe/Jersey)
(Europe/Podgorica, America/Marigot, Europe/Skopje, Europe/Ljubljana)
(Arctic/Longyearbyen, Europe/Bratislava, Europe/San_Marino)
(America/Lower_Princes, Europe/Vatican):
Undo recent changes, going back to the way these entries were done
in the last tz distribution.  Only the Antarctica/South_Pole change
was retained.