[tz] [PATCH] tzdata: Asia/Ha_Noi: Add new timezone

[Paul Eggert]

Trần Ngọc Quân wrote:

> I find an other book about this topic:

Yes, there are a lot of books on Vietnamese dates and times!  All in Vietnamese, 
unfortunately for me.  The book by Trần Ngọc Quân appears to be one of the most 
authoritative.  Dershowitz and Reingold cites its 2005 edition in their book 
Calendrical Calculations (3rd ed.) 
<http://emr.cs.iit.edu/home/reingold/calendar-book/third-edition/>.  They also 
cite the 2000 edition of a calendrical book by L T Lân and personal 
communications from Hồ Ngọc Đức -- none of which agree exactly, unfortunately.

 > This is Hanoi, not Ho Chi Minh City.

We need to correct the Asia/Ho_Chi_Minh entry regardless of what we do about 
Hanoi, and that is what the patch does.  As I pointed out in my most recent 
email, it appears to be unnecessary to add an entry for Hanoi, since Hanoi does 
not have a unique time zone history since 1970.  In contrast, Ho Chi Minh City 
(now that its data are corrected) does have a unique time zone history since 
1970 and therefore needs a distinct Zone.

I had planned to replace the Ho Chi Minh City zone with a link on the grounds 
that it was redundant, but this new information means we need to keep it.