This is an updated patch from pull request #16 which will throw an
exception if coro is called without starting the event_loop(). The
main update is to bring it up to date with recent changes and make
the linux poller throw the correct exception in this case.

flag readv() as not implemented.

The linux poller was not cleaning up the inserted wait_for event
when a poller timeout occurred. This fixes the SimultaneousError
when using with_timeout() (fixes #57).

Need to make test_notify_of_close work cross-platform.