Fix socket(fileno=fd) by auto-detecting the socket's family, type,
and proto from the file descriptor. The auto-detection can be overruled
by passing in family, type, and proto explicitly.

Without the fix, all socket except for TCP/IP over IPv4 are basically broken:

>>> s = socket.create_connection(('www.python.org', 443))
>>> s
<socket.socket fd=3, family=AddressFamily.AF_INET6, type=SocketKind.SOCK_STREAM, proto=6, laddr=('2003:58:bc4a:3b00:56ee:75ff:fe47:ca7b', 59730, 0, 0), raddr=('2a04:4e42:1b::223', 443, 0, 0)>
>>> socket.socket(fileno=s.fileno())
<socket.socket fd=3, family=AddressFamily.AF_INET, type=SocketKind.SOCK_STREAM, proto=0, laddr=('2003:58:bc4a:3b00::%2550471192', 59730, 0, 2550471192), raddr=('2a04:4e42:1b:0:700c:e70b:ff7f:0%2550471192', 443, 0, 2550471192)>
Signed-off-by: Christian Heimes <christian@python.org>

* Fix memory leaks and error handling in posix spawn
* Improve error handling when destroying the file_actions object
* Py_DECREF the result of PySequence_Fast on error
* Handle uninitialized pid
* Use OSError if file actions fails to initialize
* Move _file_actions to outer scope to avoid undefined behaviour
* Remove HAVE_POSIX_SPAWN define in Modules/posixmodule.c
* Unshadow exception and clean error message

When the C imp module became _imp in 6f44d66b, the initialization function should have been renamed from PyInit_imp to PyInit__imp.

The commit removes one unnecessary "if" clause in genobject.c.  That "if" clause was masking un-awaited coroutines warnings just to make writing unittests more convenient.

Correctly handle addresses whose username is an empty quoted string.

Add test cases for IDNA 2003 and 2008 host names. IDNA 2003
internationalized host names are working since bpo-31399 has landed. IDNA
2008 deviations are still broken and will be fixed in another patch.
Signed-off-by: Christian Heimes <christian@python.org>

Until now Python used a hard coded white list of default TLS cipher
suites. The old approach has multiple downsides. OpenSSL's default
selection was completely overruled. Python did neither benefit from new
cipher suites (ChaCha20, TLS 1.3 suites) nor blacklisted cipher suites.
For example we used to re-enable 3DES.

Python now defaults to OpenSSL DEFAULT cipher suite selection and black
lists all unwanted ciphers. Downstream vendors can override the default
cipher list with --with-ssl-default-suites.
Signed-off-by: Christian Heimes <christian@python.org>

This test is unstable and currently prevents to make any new change
since the test always fails on Travis CI.

Skip the test to get more time to fix it.

socketserver.ForkingMixIn.server_close() and
socketserver.ThreadingMixIn.server_close() now waits until all child
processes and non-daemonic threads complete.

The GIL is no longer created "on demand" to fix a race condition when
PyGILState_Ensure() is called in a non-Python thread.

To mitigate the situation when the buildbot is under load
and is unable to send/receive data fast enough:

* reduce the size of the payload
* set a generous timeout for socket ops

Add os.posix_spawn to wrap the low level POSIX API of the same name.

Contributed by Pablo Galindo.

Document the error return of PyLong_As* APIs.

A frequent Python C API usage error is neglecting to check the return
value and/or PyErr_Occurred().

This reverts commit 47c0b1f7.

Definition order of kwonly params is now guaranteed preserved.

I've run some tests on 3.7 asyncio and it appears that too many
things assume that run_in_executor returns a Future.

Ensure that ``truncate()`` preserves the file position (as reported by ``tell()``) after writes longer than the buffer size. 

It will be triggered when propagating an exception.