[tz] Inconsistencies between backward and backzone

[Benjamin Drung]

Hi,

building tz with PACKRATDATA=backzone should result in time zones that
only differ for dates before 1970. For dates after 1970 they should be
identical to not building with PACKRATDATA=backzone (using backzone to
create symlinks).

But there are four (five if you include Pacific/Enderbury) time zones
that has different UTC offset nowadays:

* America/Ensenada differs from America/Tijuana
* Asia/Kashgar differs from Asia/Urumqi
* Atlantic/Jan_Mayen differs from Europe/Berlin
* Europe/Tiraspol differs from Europe/Chisinau

First investigation indicate that the timezones in backzone did not get
the recent updates applied to them.

-- 
Benjamin Drung
Debian & Ubuntu Developer