* bpo-28087: Skip test_asyncore and test_eintr poll failures on macOS

Skip some tests of select.poll when running on macOS due to unresolved
issues with the underlying system poll function on some macOS versions.

(cherry picked from commit de046446)

* Fix socket leaks

* Fixed sockets leak

(cherry picked from commit 576def09)

(cherry picked from commit a6b4e1902250d6f28ca6d083ce1c8d7e9b91974b)

s/keys and elements/keys and values/
(cherry picked from commit cdcac039)

Fix the use of recursion in itertools.chain.from_iterable. Using recursion
is unnecessary, and can easily cause stack overflows, especially when
building in low optimization modes or with Py_DEBUG enabled.
(cherry picked from commit 5466d4af)

when pass indices of wrong type.
(cherry picked from commit d4edfc9a)
(cherry picked from commit bf4bb2e43030661e568d5d4b046e8b9351cc164c)

(cherry picked from commit c3c7ef08)

(cherry picked from commit 0ae7c8bd)

The presence of the ``--enable-optimizations`` flag is indicated by the
value of ``$enableval``, but the configure script was checking ``$withval``,
resulting in the ``--enable-optimizations`` flag being effectively ignored.
(cherry picked from commit 8cea5929)

Instead have gcc be used for the coverage build so gcc is exercised in at least one place.
(cherry picked from commit ad2f9e2c)

* bpo-29861: release references to multiprocessing Pool tasks (#743)

* bpo-29861: release references to multiprocessing Pool tasks

Release references to tasks, their arguments and their results as soon
as they are finished, instead of keeping them alive until another task
arrives.

* Comments in test

(cherry picked from commit 8988945c)

* Fix Misc/NEWS ?

From Shifted Dxit -> Shifted Exit in Doc/library/curses.rst
(cherry picked from commit 64508780)

The $CXX environment variable is not exported under the 'c' language on Travis.
(cherry picked from commit 77ed1155)

This will eliminate one of the builds in Travis, allowing for CI overall to complete faster.
(cherry picked from commit 993d4b34)

too many objects.

In git worktree directories, `.git` is a configuration
file rather than a subdirectory
(cherry picked from commit 6a6d0906)

Additional changes needed to backport:

- dropped legacy SVN support from patchcheck
- use subprocess.PIPE to silence expected error output
- don't try to use subprocess.Popen as a context manager
- don't try to pass a keyword argument to str.split()

(cherry picked from commit 482f7a27)

see [bpo-29772](http://bugs.python.org/issue29772)

(cherry picked from commit 22e707fa)

Original patch by Matthias Bussonnier.
(cherry picked from commit 160edb43)

Without this option, AppVeyor log is too unreadable.
(cherry picked from commit 8886d5f3)

* bpo-27593: Updates Windows build to use information from git (#262)

* bpo-27593: Updates Windows build to use information from git

* Fixes git command (#451)

(cherry picked from commit 8eb531d9)

(cherry picked from commit ed6795e4)