logger.go
func (l *logger) Debugf(format string, vals ...interface{}) {
	l.mut.Lock()
	defer l.mut.Unlock()
	s := fmt.Sprintf(format, vals...)
	l.logger.Output(2, "DEBUG: "+s)
	l.callHandlers(LevelDebug, s)
}
func (l *logger) Debugf(format string, vals ...interface{}) {
	l.mut.Lock()
	defer l.mut.Unlock()
	s := fmt.Sprintf(format, vals...)
	l.logger.Output(2, "DEBUG: "+s)
	l.callHandlers(LevelDebug, s)
}
// Debugf logs a formatted line with a DEBUG prefix.