io.c:1948
static void
pipe_del_fptr(fptr)
    OpenFile *fptr;
{
    struct pipe_list *list = pipe_list;
    struct pipe_list *tmp;

    if (list->fptr == fptr) {
	pipe_list = list->next;
	free(list);
	return;
    }

    while (list->next) {
	if (list->next->fptr == fptr) {
	    tmp = list->next;
	    list->next = list->next->next;
	    free(tmp);
	    return;
	}
	list = list->next;
    }
}
