More than muscle, more than speed, more than a lefty forehand so rank with topspin that it could singe the hair off your arm as it whizzes by, Rafael Nadal’s trademark is his unwillingness to relent. So on Monday at his favorite tournament, where the roughly 15,000 packed into the main stadium at Roland Garros had been chanting his name, he said “au revoir,” not “adieu” — until we see each other again.