pgsql: Sync our copy of the timezone library with IANA release tzcode20

Sync our copy of the timezone library with IANA release tzcode2016g.

This is mostly to absorb some corner-case fixes in zic for year-2037
timestamps.  The other changes that have been made are unlikely to affect
our usage, but nonetheless we may as well take 'em.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/f3094920a567cde6c86adf36a1a033d7431b11ff

Modified Files
--------------
src/timezone/localtime.c |   5 +-
src/timezone/private.h   |   1 +
src/timezone/strftime.c  |   2 +-
src/timezone/zic.c       | 440 ++++++++++++++++++++++++++---------------------
4 files changed, 250 insertions(+), 198 deletions(-)