[3.6] bpo-30595: Fix multiprocessing.Queue.get(timeout) (#2027) (#2881)

[3.6] bpo-30595: Fix multiprocessing.Queue.get(timeout) (#2027) (#2881)

* bpo-30595: Fix multiprocessing.Queue.get(timeout) (#2027)

multiprocessing.Queue.get() with a timeout now polls its reader in
non-blocking mode if it succeeded to aquire the lock but the acquire
took longer than the timeout.

Co-Authored-By: Grzegorz Grzywacz <grzgrzgrz3@gmail.com>
(cherry picked from commit 1b7863c3b6519c6e134c28cab8b8af0dea43e375)

* bpo-30595: Increase test_queue_feeder_donot_stop_onexc() timeout (#2148)

_test_multiprocessing.test_queue_feeder_donot_stop_onexc() now uses a
timeout of 1 second on Queue.get(), instead of 0.1 second, for slow
buildbots.
(cherry picked from commit 8f6eeaf21cdf4aea25fdefeec814a1ce07453fe9)