bpo-33614: Ensures module definition files for the stable ABI on Windows are correctly regenerated. (GH-7165)

Using -w, when failing tests are re-run in verbose mode, display
again the tests results at the end.

In this commit:

* Support BufferedProtocol in set_protocol() and start_tls()
* Fix proactor to cancel readers reliably
* Update tests to be compatible with OpenSSL 1.1.1
* Clarify BufferedProtocol docs
* Bump TLS tests timeouts to 60 seconds; eliminate possible race from start_serving
* Rewrite test_start_tls_server_1

Fixed bug where calling write_eof() on a _SelectorSocketTransport after
it's already closed raises AttributeError.

The failure may be due to the use oF ZFS, a case we already ignore
for Solaris-based systems where ZFS is frequently used.

Pickles of type variables and subscripted generics are now future-proof
and compatible with older Python versions.

runtest_mp.py: call print() with flush=True.

Use uuid_enc_be() if available to encode UUID to bytes as big endian.

bpo-32374, bpo-33629: Use support.SuppressCrashReport() in
test_bad_traverse() of MultiPhaseExtensionModuleTests to prevent
leaking a core dump file.

* Fixed a leak when the GC fails to add an object with __del__ into
  the gc.garbage list.
* PyGC_Collect() can now be called when an exception is set and
  preserves it.
* Fixed an undefined behavior with comparing a dead pointer with NULL.

bpo-26510 in 3.7.0a2 changed the behavior of argparse to make
subparsers required by default, returning to the behavior of 2.7
and 3.2. The behavior was changed in 3.3 to be no longer required.
While it might make more sense to have the default to required,
compatibility with 3.3 through 3.6 is probably less disruptive
than trying to reintroduce compatibility with 2.7 at this point.
This change restores the 3.6 behavior.

Add a new block_on_close class attribute to ForkingMixIn and
ThreadingMixIn classes of socketserver to opt-in for pre-3.7 behaviour.

bpo-32622, bpo-33353: On macOS, sock.connect() changes the
SO_SNDBUF value. Only set SO_SNDBUF and SO_RCVBUF buffer sizes
once a socket is connected or binded, not before.

bpo-32622, bpo-33353: sendfile() tests of test_asyncio use socket
buffers of 1 kB "to test on relative small data sets". Send only
160 KiB rather 10 MB to make the test much faster.

Shrink also SendfileBase.DATA from 1600 KiB to 160 KiB.

On Linux, 3 test_sock_sendfile_mix_with_regular_send() runs now take
less than 1 second, instead of 18 seconds.

On FreeBSD, the 3 tests didn't hang, but took 3 minutes. Now
the 3 tests pass in less than 1 seconds.

TLS 1.3 behaves slightly different than TLS 1.2. Session tickets and TLS
client cert auth are now handled after the initialy handshake. Tests now
either send/recv data to trigger session and client certs. Or tests
ignore ConnectionResetError / BrokenPipeError on the server side to
handle clients that force-close the socket fd.

To test TLS 1.3, OpenSSL 1.1.1-pre7-dev (git master + OpenSSL PR
https://github.com/openssl/openssl/pull/6340) is required.
Signed-off-by: Christian Heimes <christian@python.org>

bpo-25612, bpo-33612: Remove an assertion from PyThreadState_Clear()
which failed at Python shutdown or on fork if a thread was running a
generator.

bpo-33604: Bump removal notice from 3.6 to 3.8 and change PendingDeprecationWarning to DeprecationWarning as we had intended to do earlier...

Change TLS 1.3 cipher suite settings for compatibility with OpenSSL
1.1.1-pre6 and newer. OpenSSL 1.1.1 will have TLS 1.3 cipers enabled by
default.

Also update multissltests and Travis config to test with latest OpenSSL.
Signed-off-by: Christian Heimes <christian@python.org>

unittest.mock.MagicMock now supports the __round__() magic method.

* Set the limited API version for PyImport_GetModule and PyOS_*Fork
  functions.
* Add PyImport_GetModule and Py_UTF8Mode in PC/python3.def.
* Add several functions in Doc/data/refcounts.dat.