* zdump.8: Fix documentation of zdump cutoff behavior.

(Thanks to Tim Parenti for reporting the problem.)
Fix 2014g regression: localtime and mktime weren't setting tzname.

In 2014g, localtime and mktime set tzname[0] and tzname[1] as if by
tzset, regardless of the requested time stamp.  In 2014f and earlier,
localtime and mktime then set tzname[0] or tzname[1] to a time zone
appropriate for the time stamp in question.
Although both behaviors conform to POSIX, the 2014f behavior is
better because it lets a single-threaded application discover the
time zone abbreviation appropriate for the just-queried time stamp
even on platforms that lack TM_ZONE.  The 2014f-and-earlier zdump
relies on the 2014f library behavior on these platforms.
Problem reported by Tim Parenti in:
http://mm.icann.org/pipermail/tz/2014-September/021585.html
* localtime.c (localsub): Treat a nonzero offset value
as a request to set tzname on success.  All callers changed.
(localtime_rz, mktime_z): Define only if NETBSD_INSPIRED,
as they're no longer needed otherwise.
(localtime_tzset): Invert sense of third arg from SKIP_TZSET
to SETTZ.  New arg SETNAME.  All callers changed.
(localtime): Request tzname to be set on success.
(mktime_tzname): New function, with most of the previous
contents of mktime_z.
(mktime_z, mktime): Use it.
* NEWS: Document the above.
Fix 2014g zdump regression on platforms without TM_ZONE.

Problem reported by Tim Parenti in:
http://mm.icann.org/pipermail/tz/2014-September/021585.html
* zdump.c (localtime_r, localtime_rz) [!TM_ZONE]:
Just call 'localtime', since this can set tzname in a
timestamp-dependent way, which is better for zdump.
* NEWS: Document this.
Minor localtime fixups.

* localtime.c (localsub): Tune slightly.
Don't set tzname unless successful.
(gmtime_r, offtime, timeoff): Simplify.
* NEWS: Document the tzname change.
* NEWS, Theory, zdump.8, zic.8: Document that the proleptic Gregorian

calendar is used.  (Thanks to Alan Barrett for the suggestion.)