Issue #22641: In asyncio, the default SSL context for client connections is now created using ssl.create_default_context(), for stronger security.

* PipeServer.close() now cancels the "accept pipe" future which cancels the
  overlapped operation.
* Fix _SelectorTransport.__repr__() if the transport was closed
* Fix debug log in BaseEventLoop.create_connection(): get the socket object
  from the transport because SSL transport closes the old socket and creates a
  new SSL socket object. Remove also the _SelectorSslTransport._rawsock
  attribute: it contained the closed socket (not very useful) and it was not
  used.
* Issue #22063: socket operations (sock_recv, sock_sendall, sock_connect,
  sock_accept) of the proactor event loop don't raise an exception in debug
  mode if the socket are in blocking mode. Overlapped operations also work on
  blocking sockets.
* Fix unit tests in debug mode: mock a non-blocking socket for socket
  operations which now raise an exception if the socket is blocking.
* _fatal_error() method of _UnixReadPipeTransport and _UnixWritePipeTransport
  now log all exceptions in debug mode
* Don't log expected errors in unit tests
* Tulip issue 200: _WaitHandleFuture._unregister_wait() now catchs and logs
  exceptions.
* Tulip issue 200: Log errors in debug mode instead of simply ignoring them.

in debug mode

- Tulip issue 185: Add a create_task() method to event loops. The create_task()
  method can be overriden in custom event loop to implement their own task
  class. For example, greenio and Pulsar projects use their own task class. The
  create_task() method is now preferred over creating directly task using the
  Task class.
- tests: fix a warning
- fix typo in the name of a test function
- Update AbstractEventLoop: add new event loop methods; update also the unit test

don't log the "destroy pending task" message anymore. The log is redundant for
run_until_complete() and useless in run_briefly().

repr(Handle) is shorter for function: "foo" instead of "<function foo at
0x...>". It now also includes the source of the callback, filename and line
number where it was defined, if available.

repr(Task) now also includes the current position in the code, filename and
line number, if available. If the coroutine (generator) is done, the line
number is omitted and "done" is added.

not reliable

Use "from unittest import mock". It should simplify my work to merge new tests
in Trollius, because Trollius uses "mock" backport for Python 2.

Thanks to Vajrasky Kok for discovering some of them.

call_at() and run_in_executor() now raise a TypeError if the callback is a
coroutine function.

Thanks to Vajrasky Kok for discovering some of them.

call_at() and run_in_executor() now raise a TypeError if the callback is a
coroutine function.

Patch written by Vajrasky Kok.