tzcode: update to 2015g

Changes affecting code

localtime no longer mishandles America/Anchorage after 2037.
(Thanks to Bradley White for reporting the bug.)

On hosts with signed 32-bit time_t, localtime no longer mishandles
Pacific/Fiji after 2038-01-16 14:00 UTC.

The localtime module allows the variables 'timezone', 'daylight',
and 'altzone' to be in common storage shared with other modules,
and declares them in case the system <time.h> does not.
(Problems reported by Kees Dekker.)

On platforms with tm_zone, strftime.c now assumes it is not NULL.
This simplifies the code and is consistent with zdump.c.
(Problem reported by Christos Zoulas.)

Changes affecting documentation
The tzfile man page now documents that transition times denote the
starts (not the ends) of the corresponding time periods.
(Ambiguity reported by Bill Seymour.)

(From OE-Core master rev: 7c9082ab)

Signed-off-by: Armin Kuster <akuster808@gmail.com>
Signed-off-by: Joshua Lock <joshua.lock@collabora.co.uk>