* Failure in adding to gc.garbage is no longer fatal.
* An exception in tp_clear() no longer lead to crash (though tp_clear() should not leave exceptions).

Use transport.set_write_buffer_limits() in sendfile tests of
test_asyncio to make sure that the protocol is paused after sending
4 KiB. Previously,
test_sendfile_fallback_close_peer_in_the_middle_of_receiving() failed
on FreeBSD if the DATA was smaller than the default limit of 64 KiB.

Remove the docstring attribute of AST types and restore docstring
expression as a first stmt in their body.
Co-authored-by: INADA Naoki <methane@users.noreply.github.com>

Fix a race condition in SSLProtocol.connection_made() of
asyncio.sslproto: start immediately the handshake instead of using
call_soon(). Previously, data_received() could be called before the
handshake started, causing the handshake to hang or fail.

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.