DST and potential changes thereto

With the U.S. Government poised to tinker with Daylight Saving Time, I
have a couple questions.

0) Does PG rely on system-level TZ info or will specific updates to PG
be required?  I'm interested in *nix but the Windows folks are
probably interested, too.

1) However a change is implemented, what will be the effect on queries
for historical data? Will the localtime be correct for all dates
whether before or after the change?

Perhaps we will still dodge this bullet. But with the House and Senate
recently reaching an agreement, the change is appearing ever more
likely.

Cheers,
Steve