def recv_io(klass = IO, negotiate = true)
      write("pass IO") if negotiate
      io = @io.recv_io(klass)
      write("got IO") if negotiate
      return io
    end
def recv_io(klass = IO, negotiate = true)
      write("pass IO") if negotiate
      io = @io.recv_io(klass)
      write("got IO") if negotiate
      return io
    end
Receive an IO object (a file descriptor) from the channel. The other
 side must have sent an IO object by calling send_io(). Note that
 this only works on Unix sockets.

 Might raise SystemCallError, IOError or SocketError when something
 goes wrong.