Also fixed a few more line endings that were missed in GH-840, which were causing failure.

- new PYTHONCOERCECLOCALE config setting
- coerces legacy C locale to C.UTF-8, C.utf8 or UTF-8 by default
- always uses C.UTF-8 on Android
- uses `surrogateescape` on stdin and stdout in the coercion
  target locales
- configure option to disable locale coercion at build time
- configure option to disable C locale warning at build time

#30624 / selectors: use bare except clause in order to not leave the fd in a bad state in case of error (#2082)

Updates checked-in line endings on several files.

This PR contains two updates to typing module:

- Support ContextManager on all versions (original PR by Jelle Zijlstra).
- Add generic AsyncContextManager.

Mock os.register_at_fork() when importing the random module, since
this function doesn't allow to unregister callbacks and so leaked
memory.

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>

Running our unit tests with `-bb` enabled triggered this failure.

The function '_PyArg_ParseStack()' and
'_PyArg_UnpackStack' were failing (with error
"XXX() takes Y argument (Z given)") before
the function '_PyArg_NoStackKeywords()' was called.
Thus, the latter did not raise its more meaningful
error : "XXX() takes no keyword arguments".

Mention that fnmatchcase does not call normcase, and fnmatch does.

* asyncio SSL contexts leak sockets after calling close with certain servers

* cleanup _shutdown_timeout_handle on _fatal_error

This will allow for centralized management of the Codecov config to prevent skew as well as easier management going forward.

Closes python/core-workflow#81.

Document that assertNotRegexpMatches is a deprecated alias for assertNotRegex.

* #30014: make selectors.DefaultSelector.modify() faster by relying on selector's modify() method instead of un/register()ing the fd

* #30014: add unit test

* speedup poll/epoll/devpoll modify() method by using internal modify() call

* update doc

* address PR comments

* update NEWS entries

* use != instead of 'is not'

Avoid a deadlock when the waiter who is about to take the lock is
cancelled

Issue #27585

* Fix regression in error message introduced in bpo-29951.

* Add test.

* Make the test more strong.

contextlib.AbstractContextManager now supports anti-registration
by setting __enter__ = None or __exit__ = None, following the pattern
introduced in bpo-25958.

Test C functions:

* _PyObject_FastCall()
* _PyObject_FastCallDict()
* _PyObject_FastCallKeywords()

* RFC 1750 has been been obsoleted by RFC 4086.
* RFC 3280 has been obsoleted by RFC 5280.
* RFC 4366 has been obsoleted by RFC 6066.

See discussion:
  https://github.com/python/cpython/pull/1992#issuecomment-307024778

* Add a new option taking a filename to get a list of test names to
  filter tests.
* support.match_tests becomes a list.
* Modify run_unittest() to accept to match the whole test identifier,
  not just a part of a test identifier.

For example, the following command only runs test_default_timeout()
of the BarrierTests class of test_threading:

$ ./python -m test -v test_threading -m test.test_threading.BarrierTests.test_default_timeout

Remove also some empty lines from test_regrtest.py to make flake8
tool happy.

'invalid character in identifier' now is raised instead of
'f-string: empty expression not allowed' if a subexpression contains
only whitespaces and they are not accepted by Python parser.

Fix a reference leak in _io._WindowsConsoleIO: PyUnicode_FSDecoder()
always initialize decodedname when it succeed and it doesn't clear
input decodedname object.

On Windows, subprocess.Popen.communicate() now also ignore EINVAL
on stdin.write() if the child process is still running but closed the
pipe.

The cell_contents attribute of the cell object is now writable.

Error messages when pass keyword arguments to some builtins that
don't support keyword arguments contained double parenthesis: "()()".
The regression was introduced by bpo-30534.