This change fixes a race conditon related to _WaitHandleFuture.cancel() leading
to Python crash or "GetQueuedCompletionStatus() returned an unexpected event"
logs. Before, the overlapped object was destroyed too early, it was possible
that the wait completed whereas the overlapped object was already destroyed.
Sometimes, a different overlapped was allocated at the same address, leading to
unexpected completition.

_WaitHandleFuture.cancel() now waits until the wait is cancelled to clear its
reference to the overlapped object. To wait until the cancellation is done,
UnregisterWaitEx() is used with an event instead of UnregisterWait().

To wait for this event, a new _WaitCancelFuture class was added. It's a
simplified version of _WaitCancelFuture. For example, its cancel() method calls
UnregisterWait(), not UnregisterWaitEx(). _WaitCancelFuture should not be
cancelled.

The overlapped object is kept alive in _WaitHandleFuture until the wait is
unregistered.

Other changes:

* Add _overlapped.UnregisterWaitEx()
* Remove fast-path in IocpProactor.wait_for_handle() to immediatly set the
  result if the wait already completed. I'm not sure that it's safe to
  call immediatly UnregisterWaitEx() before the completion was signaled.
* Add IocpProactor._unregistered() to forget an overlapped which may never be
  signaled, but may be signaled for the next loop iteration. It avoids to
  block forever IocpProactor.close() if a wait was cancelled, and it may also
  avoid some "... unexpected event ..." warnings.

tests: Remove unused function; inline another function

* Handle correctly CancelledError: just exit
* On error, log the exception and exit

Don't try to close the event loop, it is probably running and so it cannot be
closed.

Python subprocess failure assertion error messages for easier debugging.

Adds a unittest for test.script_helper to confirm that this code works as
it is otherwise uncovered by an already passing test suite that uses it. :)

Python subprocess failure assertion error messages for easier debugging.

Adds a unittest for test.script_helper to confirm that this code works as
it is otherwise uncovered by an already passing test suite that uses it. :)

Noticed by Martin Panter.

Patch by Mike Short.

Patch by Mike Short.

This commit also removes a couple of non-standard status codes. They were
added as part of edf669b13482, so there is no backwards compatibility issue.

Patch by Demian Brecht.

Elsewhere in the setobject.c code we do a bitwise-and with the mask
instead of using a conditional to reset to zero on wrap-around.
Using that same technique here use gives cleaner, faster, and more
consistent code.

duplicated addresses and simplify the code.

Issue 23261:  Clean-up the hack to store the set.pop() search finger in a hash field instead of the setobject.

portable representation.

Issue #23266: Much faster implementation of ipaddress.collapse_addresses() when there are many non-consecutive addresses.

Patch by Al Sweigart.

getaddrinfo("localhost") can fail depending on the name server configuration,
use "127.0.0.0" instead.

Issue #21817: When an exception is raised in a task submitted to a ProcessPoolExecutor, the remote traceback is now displayed in the parent process.
Patch by Claudiu Popa.

Patch by Nikolaus Rath and Martin Panter.

Only happened with oddly capitalized debug executables on Windows.
Patch by Claudiu Popa.

Patch by Jon Dufresne.