asyncio: Don't special-case GeneratorExit in Condition.wait().
asyncio: Tiny cleanup in streams.py.
asyncio: Fix race in subprocess transport, by Victor Stinner.
asyncio: Minimal pty support in UNIX read pipe, by Jonathan Slenders.
Try to fix some ttk tests.  Error messages were changed in 8.6b3.
Try to fix some ttk tests.  Error messages were changed in 8.6b3.
Cleanup properly proactor event loop

* store the "self reading" future when the "self pipe" is closed (when the
  event loop is closed)
* store "accept" futures to cancel them when we stop serving
* close the "accept socket" if the "accept future" is cancelled

Fix many warnings which can be seen when unit tests are run in verbose mode.
Fix ResourceWarning in test_asyncio.test_windows_events:
close the write end of the socket pair