Oh, another thought here: what is the effect of the combination of this
with your other proposal to add more timezones to the list? In
particular, what happens if we use the extended list in an unpatched
system that doesn't know about those new zone names? I'm wondering
if we *have* to make this change for that to behave sanely. We might
also need to consider whether we want any log chatter in such a case.
regards, tom lane