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.

fixes #58. Added proper check for libaio

Add asynchronous disk io support on Linux (aio_read/aio_write) through libaio

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diffie-hellman: do not send_newkeys() in response to kexdh_reply