Catch up to current for the following, requested by kre in ticket #1634:

external/public-domain/tz/dist/Makefile        up to 1.1.1.21
external/public-domain/tz/dist/NEWS            up to 1.1.1.22
external/public-domain/tz/dist/TZDATA_VERSION  up to 1.12
external/public-domain/tz/dist/africa          up to 1.1.1.15
external/public-domain/tz/dist/asia            up to 1.1.1.20
external/public-domain/tz/dist/australasia      up to 1.1.1.15
external/public-domain/tz/dist/europe          up to 1.1.1.21
external/public-domain/tz/dist/theory.html      up to 1.1.1.4
external/public-domain/tz/dist/version          up to 1.1.1.9
external/public-domain/tz/dist/ziguard.awk      up to 1.1.1.2
doc/3RDPARTY 1.1520 (patch)

Import tzdata2018e from ftp://ftp.iana.org/tz/releases/tzdata2018e.tar.gz

Summary of changes in tzdata2018e (2018-05-01 23:42:51 -0700):

News for the tz database

Release 2018e - 2018-05-01 23:42:51 -0700

    North Korea switches back to +09 on 2018-05-05 (tomorrow!)

(martin)