zdump.8: Sync from tzdb upstream

zdump.8: Sync from tzdb upstream

Make zdump.8 a copy of the upstream tzdb version, except that
the tzdb version's first line is replaced by man-pages
boilerplate.

This has the following effect:

Document new options -i, -t, -V.

New section LIMITATIONS.

Do some minor reformatting.

Omit some changes that were made on the man-pages side, notably by
changing some "timezone"s back to the preferred-upstream "time
zone" when talking about traditional time zones as opposed to
POSIX timezone settings.  Also, fix some formatting glitches.

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>