[tz] [PROPOSED] Support zi parsers that mishandle negative DST offsets

[Paul Eggert]

Stephen Colebourne wrote:

> you are
> effectively asking some of its key consumers to fork the project. I
> find that pretty astonishing.

I would find it astonishing too, if that was what was being suggested. But it's 
not. I'm merely suggesting standard practice that is commonly done by other tzdb 
consumers. For example, you can see it in action here:

https://packages.debian.org/sid/tzdata

This currently contains a copy of tzdata 2018c, along with a small patch that 
supplies some time zone links (e.g., SystemV/AST4ADT) that were removed from 
tzdata in release 2005p, links that Debian kept due to compatibility concerns. 
This is not a fork of the project in any real sense; it's just routine shimming.
> there is absolutely no good rationale for making this change

Although there is good rationale for the change, you clearly disagree. 
Similarly, back in 2005 there was good rationale to remove SystemV/AST4ADT and 
clearly not everyone agreed. There was a reasonable approach back then to 
accommodate that disagreement, and a similar approach would work well here too. 
After all, it's simply not practical to insist on complete lock-step agreement 
among all tzdata consumers.