asyncio: sync with Tulip

--HG--
branch : 3.4
asyncio: sync with Tulip

* Fix a race condition in BaseSubprocessTransport._try_finish().

  If the process exited before the _post_init() method was called, scheduling
  the call to _call_connection_lost() with call_soon() is wrong:
  connection_made() must be called before connection_lost().

  Reuse the BaseSubprocessTransport._call() method to schedule the call to
  _call_connection_lost() to ensure that connection_made() and
  connection_lost() are called in the correct order.

* Add repr(PipeHandle)

* Fix typo

--HG--
branch : 3.4