[tz] suggestion: split "backward" into "backward" and "deprecated"

[Tom Lane]

I wrote:
> It's not clear to me whether your proposal includes removal of the
> newly "deprecated" zones from the default build rule.

After further thought I've concluded that I don't like Andrew's
proposal as-presented.  If some zone names are moved into a new
source file, what will inevitably happen is that some platforms/
repackagers will continue to support those names, while others
will not --- either through conscious choice or just by forgetting
to update their build recipes.  That seems like a bad situation
to create.  Like it or not, tzdb has created a de facto standard
for the set of known zone names, and it's better for a standard
to be actually standard, not subject to local whims.  Recall that
in the other thread Andrew referred to, FreeBSD got ragged on for
being the only major platform not supporting the "backward" zones.
That was justifiable IMO, and I don't think that situation should
be reintroduced or magnified.

Thus, I think it would be better to either do nothing, or decide
that these zone names are dead, and summarily remove them altogether.
While the latter option would no doubt cause some pain somewhere,
it's not without precedent.  I compare it to the effort not so long
ago to remove undocumented zone abbreviations.  That did result in
some push-back, but not a huge amount ... and what's more to the point
for the current discussion, downstream packagers were not given any
choice in the matter.

In short, I don't care hugely whether these zone names live or die;
but let's either kill them off everywhere or nowhere.

			regards, tom lane