rem: int fd = io_out_fd;
add: int fd = multiplex_out_fd;
context: void io_flush(void){	int fd = io_out_fd;	if (!io_buffer_count) return;	if (io_multiplexing_out) {		SIVAL(io_buffer-4, 0, (MPLEX_BASE<<24) + io_buffer_count);		if (writefd_unbuffered(fd, io_buffer-4, io_buffer_count+4) !=		    io_buffer_count+4) {			rprintf(FERROR,"write failed\n");			exit_cleanup(1);		}	} else {		if (writefd_unbuffered(fd, io_buffer, io_buffer_count) != 		    io_buffer_count) {			rprintf(FERROR,"write failed\n");			exit_cleanup(1);		}	}	io_buffer_count = 0;}