When graceful shutdown was requested, and then nginx was forced to
do fast shutdown, it used to (incorrectly) complain about open sockets
left in connections which weren't yet closed when fast shutdown
was requested.

Fix is to avoid complaining about open sockets when fast shutdown was
requested after graceful one.  Abnormal termination, if requested with
the WINCH signal, can still happen though.

Previously, if an event was posted by a read event handler, called by
ngx_close_idle_connections(), that event was not processed until the next
event loop iteration, which could happen after a timeout.

On some systems, it's possible that reaper of orphaned processes is
set to something other than "init" process.  On such systems, the
changing binary procedure did not work.

The fix is to check if PPID has changed, instead of assuming it's
always 1 for orphaned processes.

The directive configures a timeout to be used when gracefully shutting down
worker processes.  When the timer expires, nginx will try to close all
the connections currently open to facilitate shutdown.

There is no need to cancel timers early if there are other timers blocking
shutdown anyway.  Preserving such timers allows nginx to continue some
periodic work till the shutdown is actually possible.

With the new approach, timers with ev->cancelable are simply ignored when
checking if there are any timers left during shutdown.

The new parameters "manager_files", "manager_sleep"
and "manager_threshold" were added to proxy_cache_path
and friends.

Note that ngx_path_manager_pt was changed to return ngx_msec_t
instead of time_t (API change).

The change in b91bcba29351 was not enough to fix random() seeding.
On Windows, the srand() seeds the PRNG only in the current thread,
and worse, is not inherited from the calling thread.  Due to this,
worker threads were not properly seeded.

Reported by Marc Bevand.

It is implied for "x" and "X".