proposed tz changes (zdump.c, backward, and systemv)

[Olson, Arthur David (NIH/NCI)]

I'll hold off on changing backward and systemv in the upcoming Monday
distribution; it's important to get other changes out at that point
since some of them effect current clocks.

The best approach to take on the systemv stuff may be to simply
eliminate it from the distribution. The systemv stuff was included way
back in 1986 when System V was still relevant; twenty years later it can
presumably be dispensed with.

On the backward side: a characteristic of the time zone compiler is that
it doesn't clear out the destination directory before putting results
there, so existing files remain unless they're replaced. Further, if a
binary file exists with a name that matches that of the TZ environment
variable, the data in the binary file is used even if the TZ value is
something such as "EST5EDT". So we do want to generate binary files for
EST5EDT et al. to ensure that no bad data remains in the destination
directory. To avoid having US rules in both "northamerica" and
"backward" (introducing the possibility that the rules get out of sync),
we could put the "Zone EST5EDT ..." stuff in the northamerica file
(where the US rules currently appear).

If we do end up with two copies of the US rules, we'll want to make sure
that there's a comment with each copy indicating the need to keep it in
sync with the other copy.

				--ado