This reverts commit 1596d323 since
it broke cluster startup, clearly it needs more attention before
being ready.

This puts on on par with upstream PostgreSQL 9.1.20, released on
2016-02-11, for tzdata and the below referenced commit. The reason
for not updating further is that there are tzdata format changes
in 9.1.21, 2016a is the last release we can import without merging
code changes as well.

  commit 6887d72d06a2f36508d5be9cca316088d4c60b26
  Author: Tom Lane <tgl@sss.pgh.pa.us>
  Date:   Fri Feb 5 10:59:09 2016 -0500

    Update time zone data files to tzdata release 2016a.

    DST law changes in Cayman Islands, Metlakatla, Trans-Baikal Territory
    (Zabaykalsky Krai).  Historical corrections for Pakistan.

to the Default timezone abbreviation set.

Back-port the the current file set to all branches that contain tznames.
This includes adding SGT to the Default set in pre-8.4 releases.

Joachim Wieland

Mauritius began using DST in the summer 2008-2009; the Olson library has been
updated already.

Xavier Bugaud

Add $PostgreSQL$ lines for CVS identity, too.

configuration files that can be altered by a DBA.  The australian_timezones
GUC setting disappears, replaced by a timezone_abbreviations setting (set this
to 'Australia' to get the effect of australian_timezones).  The list of zone
names defined by default has undergone a bit of cleanup, too.  Documentation
still needs some work --- in particular, should we fix Table B-4, or just get
rid of it?  Joachim Wieland, with some editorializing by moi.