why the different MST7MDT zoneinfo files?

[Paul Eggert]

> Date: Sun, 24 Dec 2000 10:41:17 -0500
> From: Ben Collins <bcollins at debian.org>
> 
> I'm not too familiar with zoneinfo symantics, but I need to follow up on
> a Debian bug report. A user noticed these different MST7MDT zoneinfo
> files, and that the SystemV ones have the incorrect DST. Why are they
> different? Shouldn't the all be the same?
> 
> f1937d0d3ed3a6cf9ca44e04cb4d8509  /usr/share/zoneinfo/MST7MDT
> f1937d0d3ed3a6cf9ca44e04cb4d8509  /usr/share/zoneinfo/posix/MST7MDT
> 1ac36e9eb32fbeb87af9921ba5b58850  /usr/share/zoneinfo/posix/SystemV/MST7MDT
> 65cbdc206e84bf90b10fabb30c13e9b1  /usr/share/zoneinfo/right/MST7MDT
> b4885b6a643d6a8c6e5e1f7de5180650  /usr/share/zoneinfo/right/SystemV/MST7MDT
> 1ac36e9eb32fbeb87af9921ba5b58850  /usr/share/zoneinfo/SystemV/MST7MDT

The SystemV stuff is for compatibility with ancient hosts, none of
which must be operating any more, as they mishandle US daylight saving
time past 1987.  We should obsolete those entries, for the same reason
that US/Pacific-PET was removed in 1994: they are far more likely to
cause problems than to solve them.

The "posix" vs "right" difference is for leap second support.
"posix" ignores leap seconds, whereas "right" does not.

I suppose we shouldn't just remove the SystemV stuff right away, as
there might be some hosts that (mistakenly) use it.  But my next
proposed patch can replace it with this for now:

Link	America/Halifax		SystemV/AST4ADT
Link	America/New_York	SystemV/EST5EDT
Link	America/Chicago		SystemV/CST6CDT
Link	America/Denver		SystemV/MST7MDT
Link	America/Los_Angeles	SystemV/PST8PDT
Link	America/Anchorage	SystemV/YST9YDT
Link	America/Puerto_Rico	SystemV/AST4
Link	America/Indianapolis	SystemV/EST5
Link	America/Regina		SystemV/CST6
Link	America/Phoenix		SystemV/MST7
Link	Pacific/Pitcairn	SystemV/PST8
Link	Pacific/Gambier		SystemV/YST9
Link	America/Honolulu	SystemV/HST10