Sync zoneinfo database with tzdata2015b from ftp://ftp.iana.org/tz/releases

Sync zoneinfo database with tzdata2015b from ftp://ftp.iana.org/tz/releases

Changes affecting future time stamps

* Mongolia will start observing DST again this year, from the last Saturday
  in March at 02:00 to the last Saturday in September at 00:00.
  (Thanks to Ganbold Tsagaankhuu.)

* Palestine will start DST on March 28, not March 27.  Also,
    correct the fall 2014 transition from September 26 to October 24.
    Adjust future predictions accordingly.  (Thanks to Steffen Thorsen.)

Changes affecting past time stamps

* The 1982 zone shift in Pacific/Easter has been corrected, fixing a 2015a
    regression.  (Thanks to Stuart Bishop for reporting the problem.)

* Some more zones have been turned into links, when they differed
    from existing zones only for older time stamps.  As usual,
    these changes affect UTC offsets in pre-1970 time stamps only.
    The affected zones are: America/Antigua, America/Cayman,
    Pacific/Midway, and Pacific/Saipan.

Changes affecting time zone abbreviations

* Correct the 1992-2010 DST abbreviation in Volgograd from "MSK" to "MSD".
    (Thanks to Hank W.)

Changes affecting commentary

* Cite the recent Mexican decree changing Quintana Roo's time zone.
    (Thanks to Carlos Raúl Perasso.)

* Likewise for the recent Chilean decree.  (Thanks to Eduardo Romero Urra.)

* Update info about Mars time.