This gets the time zone abbreviations from
https://www.timeanddate.com/time/zones/, and adds unambiguous time
zones not already present in zonetab.list.  See bin/update-abbr
for the program used.

This regenerates zonetab.h using prereq.mk (requires gperf).

Only one test line is added, just to make sure a new time zone
abbreviation is picked up.

Fixes Ruby Bug 16286

https://github.com/ruby/date/commit/702e8b3033