[tz] [PROPOSED] Support SAVE suffixes, for Namibia 1994-2017

[Paul Eggert]

Michael Deckers via tz wrote:

>     Considering that this proposal makes the setting of the dst bit
>     an issue that is independent from the circumstance of whether
>     the value of a SAVE entry is zero or not,  is it not
>     desirable to completely  avoid the use of negative SAVE values
>     to express the dst bit setting, so as to make it easier for
>     parsers of zic source files to follow the changes
>     in the "bleeding edge" format?

It's more the other way around, I would think. zic has supported negative SAVE 
values for decades and most other tzdata parsers have followed suit. So if a 
timekeeping practice can be specified either way, it'll be easier on the 
installed base if we use this long-established feature than if we use the 
proposed new feature.

I get the point that we'd rather keep the syntax simpler and more regular, and 
that lessening the number of syntax features helps do that. But here I think the 
compatibility win outweighs the regularity loss.

>     for systematicness, shouldn't the same suffixes and defaults
>     also be applicable to a numeric entry in the RULE column of
>     ZONE lines?

Good point, thanks. Proposed further patch attached.
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