[tz] Add new timezone for Hanoi Capital, Vietnam

[Guy Harris]

On Feb 18, 2019, at 10:07 AM, KP <khaiphan9x at gmail.com> wrote:

> I have a talent for continuous change of Indochina time, but it is a Vietnamese document, I have not found the same document in English. Show that the time of Vietnam taking Asia/Bangkok is wrong, because Thai does not apply under this document
> https://vi.m.wikipedia.org/wiki/Giờ_ở_Việt_Nam

See

	https://translate.google.com/translate?sl=auto&tl=en&u=https%3A%2F%2Fvi.wikipedia.org%2Fwiki%2FGiờ_ở_Việt_Nam

for the Google translation into English.

What it says about post-1970-01-01 00:00:00 UTC times is:

	Time in Northern Vietnam

		...

		January 1, 1968 - June 12, 1975	UTC + 07:00:00	Hanoi time zone

	Time in South Vietnam

		...

		January 1, 1960 - June 12, 1975	UTC + 8:00 pm	Saigon Standard Time

	The time in Vietnam is unified 

		June 13, 1975 -nay	UTC + 07:00:00	Standard time zone

with no indication about standard vs. summer time; the tzdb doesn't show Vietnam ever having seasonal time shifts, so that makes sense.  The only reference given on the page doesn't seem to, in the generated translation, address time zones at all.

And, no, it says nothing about Thailand, but, as noted, North Vietnam happened to keep the same time as Thailand from 1970 to reunification; *that's*, plus Bangkok being larger than Hanoi, why Asia/Bangkok is used as the tzdb id for that region.