Major changes:
- StreamReader.readexactly() now raises an IncompleteReadError if the
end of stream is reached before we received enough bytes, instead of
returning less bytes than requested.
- Unit tests use the main asyncio module instead of submodules like events
- _UnixWritePipeTransport now also supports character devices, as
_UnixReadPipeTransport. Patch written by Jonathan Slenders.
- Export more symbols: BaseEventLoop, BaseProactorEventLoop,
BaseSelectorEventLoop, Queue and Queue sublasses, Empty, Full
* 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.
