* backward: Move links here from other files, if the only reason
they existed was to fill out zone.tab. Zones are now allowed to
cross national borders, so a zone now need not exist merely
because there's a national border. Sort the list consistently.
None of this changes any time stamp in the database.
* checktab.awk: Don't require that zone.tab's column 3 be unique.
* europe (Europe/Jersey, Europe/Guernsey, Europe/Isle_of_Man)
(Europe/Mariehamn, Europe/Busingen, Europe/Vatican, Europe/San_Marino)
(Arctic/Longyearbyen, Europe/Ljubljana, Europe/Podgorica)
(Europe/Sarajevo, Europe/Skopje, Europe/Zagreb, Europe/Bratislava):
* northamerica (America/St_Barthelemy, America/Marigot):
* southamerica (America/Lower_Princes, America/Kralendijk):
Move links to 'backward'.
* zone.tab: Give more details about how different rows can have
duplicate column 1 or column 3. For each link moved to 'backward',
change column 3 to be the non-backward name.
