TODO item: update source/timezone for 64-bit tz files

Back when we converted src/timezone to use int64 for pg_time_t, we
wondered what to do about extending the compiled timezone data file
format for int64, so that it would work for years beyound 2038.  We
shelved the problem waiting to see what the upstream zic folks would do.
Well, it looks like they've done something about it.  So I think we
ought to plan on updating our code to match theirs, so that we fix the
y2038 problem while keeping it possible to use a standard zic-database
installation with Postgres.  This is not urgent (I surely see no need
to hold up 8.2 to fix it), but it ought to go on the TODO list.
        regards, tom lane