Issue #20510: Rewrote test_exit in test_sys to match existing comments
and to modernize.  Patch by Gareth Rees.
Issue #20510: Merge with 3.3.
asyncio: Add support for UNIX Domain Sockets.
Misc/NEWS: Add a news item for UNIX Sockets support in asyncio. Cleanup WS.
Issue #20609: Fix building 64-bit binaries on 32-bit Windows.
Issue #20609: Merge with 3.3.
Mangle __parameters in __annotations__ dict properly. Issue #20625.
asyncio: Make tests pass on Windows.
Close issue20653: allow Enum subclasses to override __reduce_ex__
Issue #19612: On Windows, subprocess.Popen.communicate() now ignores
OSError(22, 'Invalid argument') when writing input data into stdin, whereas
the process already exited.
(Merge 3.3) Issue #19612: On Windows, subprocess.Popen.communicate() now
ignores OSError(22, 'Invalid argument') when writing input data into stdin,
whereas the process already exited.
Issue #20625: Fix compilation issue
asyncio: New error handling API. Issue #20681.
asyncio.transports: Make _ProactorBasePipeTransport use _FlowControlMixin
asyncio, Tulip issue 139: Improve error messages on "fatal errors"

Mention if the error was caused by a read or a write, and be more specific on
the object (ex: "pipe transport" instead of "transport").
asyncio, Tulip issue 143: UNIX domain methods, fix ResourceWarning and
DeprecationWarning warnings. create_unix_server() closes the socket on any
error, not only on OSError.
Issue #20682: test_asyncio, _basetest_create_connection() checks also the
sockname, as _basetest_create_ssl_connection().
asyncio: Fix spelling and typos.

Thanks to Vajrasky Kok for discovering some of them.
asyncio: pep8-ify the code.