Timezone data: Update to 2015c

Timezone information is updated to 2015c, released on 14 Apr 2015.

I used build/zoneinfo2lua.pl to pull data from my Ubuntu 14.10.

Changes in 2015b and 2015c are rather small:
http://mm.icann.org/pipermail/tz-announce/2015-March/000029.html
http://mm.icann.org/pipermail/tz-announce/2015-April/000030.html

     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.

     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.

     Egypt's spring-forward transition is at 24:00 on April's last Thursday,
     not 00:00 on April's last Friday.  2015's transition will therefore be on
     Thursday, April 30 at 24:00, not Friday, April 24 at 00:00.  Similar fixes
     apply to 2026, 2037, 2043, etc.

Signed-off-by: Hannu Nyman <hannu.nyman@iki.fi>