ignores negative fd:s.
(kill_io_listen_port): New function.
(init_io_listen_port): New function.
(oop_io_accept): New function.
(io_listen): New function, replacing function in io_commands.c.
(sockaddr2info): Resurrected function. Use const sockaddr *
argument. Handle only AF_INET and AF_INET6.
(io_bind_local): Use const argument.
(io_connect_local): Likewise.

Rev: src/io.c:1.224