rem: usage_error(ErrorHandler *errh, char *error_message, ...)
add: usage_error(ErrorHandler *errh, const char *error_message, ...)
context: usage_error(ErrorHandler *errh, char *error_message, ...){    va_list val;    va_start(val, error_message);    if (!error_message)	errh->message("Usage: %s [OPTIONS] [FONTFILE [OUTPUTFILE]]", program_name);    else	errh->verror(ErrorHandler::ERR_ERROR, String(), error_message, val);    errh->message("Type %s --help for more information.", program_name);    exit(1);}