[tz] leap second theory

[Paul Eggert]

Brian Inglis wrote:
> The POSIX Austin CSRG is discussing clarifying tm_isdst:
> 
> https://www.mail-archive.com/search?q=time&l=austin-group-l%40opengroup.org

That issue was resolved last month as "Accepted as Marked". See:

http://austingroupbugs.net/view.php?id=1253

This was fallout from our June discussion, e.g.:

https://mm.icann.org/pipermail/tz/2019-June/028043.html

and the Austin Group interpretation was the expected one, e.g., tm_isdt > 0 
corresponds to the "GMT" part of the TZ setting "IST-1GMT0,M10.5.0,M3.5.0/1" 
even though its UTC offset is less than that of the "IST" part.