parameter "dontwait".
* fhandler_socket.cc (fhandler_socket::wait_for_events): Act as if the
socket is non-blocking if dontwait is true.
(fhandler_socket::recv_internal): Use incoming MSG_DONTWAIT flag to
set the wait_for_events dontwait parameter.
(fhandler_socket::send_internal): Ditto. Optimize code slightly.
* include/cygwin/socket.h (MSG_DONTWAIT): Define.
* include/cygwin/version.h: Bump API minor number.