[tz] Issues with pre-1970 information in TZDB

[Tom Lane]

I wrote:
> 1. It's not possible to separate the new backzone zones from the old.
> It's therefore impossible to generate a TZif tree that matches the
> prior dataset: you can either lose the data for the moved zones, or
> gain it back while also absorbing a whole lot of other changes of
> dubious quality.  (If they weren't dubious, they wouldn't have been
> in backzone to begin with.)  Either choice forces dubious changes to
> one or another subset of the zones.

BTW, maybe it's necessary to clarify: adding backzone to the compile
does not result in a change in the set of zone names that are generated.
What it changes is the data presented for some of the zones.

>From my perspective, it'd have been better or at least more honest
if the moved zones had disappeared from the TZif tree altogether.
It would then be apparent to end users that they were depending on a
no-longer-supported zone definition.  As-is, it's a subtle data change
that you might not notice for a really long time, leaving you with a
big mess to clean up when you do notice.

			regards, tom lane