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

Fixed create_connection() to match the emulated one.

Added "pycrypto" as the required dependency

json_rpc_remote: allow persistent http client (+ close method)

pull coro_unittest into this directory

client: getattr proxy object