Update time zone data files to tzdata release 2014h.

Most zones in the Russian Federation are subtracting one or two hours
as of 2014-10-26.  Update the meanings of the abbreviations IRKT, KRAT,
MAGT, MSK, NOVT, OMST, SAKT, VLAT, YAKT, YEKT to match.

The IANA timezone database has adopted abbreviations of the form AxST/AxDT
for all Australian time zones, reflecting what they believe to be current
majority practice Down Under.  These names do not conflict with usage
elsewhere (other than ACST for Acre Summer Time, which has been in disuse
since 1994).  Accordingly, adopt these names into our "Default" timezone
abbreviation set.  The "Australia" abbreviation set now contains only
CST,EAST,EST,SAST,SAT,WST, all of which are thought to be mostly historical
usage.  Note that SAST has also been changed to be South Africa Standard
Time in the "Default" abbreviation set.

Add zone abbreviations SRET (Asia/Srednekolymsk) and XJT (Asia/Urumqi),
and use WSST/WSDT for western Samoa.

Also a DST law change in the Turks & Caicos Islands (America/Grand_Turk),
and numerous corrections for historical time zone data.
Eliminate one background-worker-related flag variable.

Teach sigusr1_handler() to use the same test for whether a worker
might need to be started as ServerLoop().  Aside from being perhaps
a bit simpler, this prevents a potentially-unbounded delay when
starting a background worker.  On some platforms, select() doesn't
return when interrupted by a signal, but is instead restarted,
including a reset of the timeout to the originally-requested value.
If signals arrive often enough, but no connection requests arrive,
sigusr1_handler() will be executed repeatedly, but the body of
ServerLoop() won't be reached.  This change ensures that, even in
that case, background workers will eventually get launched.

This is far from a perfect fix; really, we need select() to return
control to ServerLoop() after an interrupt, either via the self-pipe
trick or some other mechanism.  But that's going to require more
work and discussion, so let's do this for now to at least mitigate
the damage.

Per investigation of test_shm_mq failures on buildfarm member anole.
Update 9.4 release notes for commits through today.

Add entries for recent changes, including noting the JSONB format change
and the recent timezone data changes.  We should remove those two items
before 9.4 final: the JSONB change will be of no interest in the long
run, and it's not normally our habit to mention timezone updates in
major-release notes.  But it seems important to document them temporarily
for beta testers.

I failed to resist the temptation to wordsmith a couple of existing
entries, too.