when there are no more `await` or `yield (from)` before return in coroutine,
cancel was ignored.

example:

    async def coro():
        asyncio.Task.current_task().cancel()
        return 42
    ...
    res = await coro()  # should raise CancelledError

This implementation provides additional 10-20% speed boost for
asyncio programs.

The patch also fixes _asynciomodule.c to use Arguments Clinic, and
makes '_schedule_callbacks' an overridable method (as it was in 3.5).

Patch by Johannes Ebke.

This is now an official "protected" API that can be used to write
classes that are duck-type-compatible with Future without subclassing
it.  (For that purpose I also changed isinstance(result, Future) to
check for this attribute instead.)

Hopefully Amber Brown can use this to make Twisted.Deferred compatible
with asyncio.Future.

Tests and docs are TBD.

It will probably be added back in Python 3.6, once its compatibility
issues are resolved; see [1] for more details.

[1] https://mail.python.org/pipermail/async-sig/2016-June/000045.html

Fix GH#325: Allow to pass None as a timeout value to disable timeout logic.

Change written by Andrew Svetlov and merged by Guido van Rossum.

See https://github.com/python/asyncio/pull/303 for details

See https://github.com/python/asyncio/pull/292 for details.

See https://github.com/python/asyncio/pull/289 for details.

* Fix ResourceWarning warnings in test_streams
* Return True from StreamReader.eof_received() to fix
  http://bugs.python.org/issue24539 (but still needs a unittest).
  Add StreamReader.__repr__() for easy debugging.
* remove unused imports
* Issue #234: Drop JoinableQueue on Python 3.5+

Move compatibility helpers for the different Python versions to a new
asyncio.compat module.

See also issue 24017.

* Cleanup gather(): use cancelled() method instead of using private Future
  attribute
* Fix _UnixReadPipeTransport and _UnixWritePipeTransport. Only start reading
  when connection_made() has been called.
* Issue #23333: Fix BaseSelectorEventLoop._accept_connection(). Close the
  transport on error. In debug mode, log errors using call_exception_handler()

* Document why set_result() calls are safe
* Cleanup gather(). Use public methods instead of hacks to consume the
  exception of a future.
* sock_connect(): pass directly the fd to _sock_connect_done instead of the
  socket.