asyncio, Tulip issue 201: Fix a race condition in wait_for()

Don't raise a TimeoutError if we reached the timeout and the future completed
in the same iteration of the event loop. A side effect of the bug is that
Queue.get() looses items.
(Merge 3.4) asyncio, Tulip issue 201: Fix a race condition in wait_for()

Don't raise a TimeoutError if we reached the timeout and the future completed
in the same iteration of the event loop. A side effect of the bug is that
Queue.get() looses items.