Update time zone data files to tzdata release 2017b.

DST law changes in Chile, Haiti, and Mongolia.  Historical corrections for
Ecuador, Kazakhstan, Liberia, and Spain.

The IANA crew continue their campaign to replace invented time zone
abbrevations with numeric GMT offsets.  This update changes numerous zones
in South America, the Pacific and Indian oceans, and some Asian and Middle
Eastern zones.  I kept these abbreviations in the tznames/ data files,
however, so that we will still accept them for input.  (We may want to
start trimming those files someday, but I think we should wait for the
upstream dust to settle before deciding what to do.)

In passing, add MESZ (Mitteleuropaeische Sommerzeit) to the tznames lists;
since we accept MEZ (Mitteleuropaeische Zeit) it seems rather strange not
to take the other one.  And fix some incorrect, or at least obsolete,
comments that certain abbreviations are not traceable to the IANA data.