new Zone Pacific/Bougainville

This is for the part of Papua New Guinea that plans to switch from
UTC+10 to UTC+11 on 2014-12-28 at 02:00.  (Thanks to Kiley Walbom
for the heads-up.)
* australasia (Pacific/Bougainville): New zone.
* zone.tab, zone1970.tab: Add entries for it.
* NEWS: Document this.