"close" terminology replaced by "stop" in nn_sock/sockbase

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>
stopped event moved from nn_sockbase to nn_sock

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>
Bug in nn_fsm fixed

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>