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