WASHINGTON (Reuters) - President-elect Barack Obama honored his vanquished Republican rival John McCain on Monday, describing the Arizona senator as an "American hero" while the Democrat prepared to assume the office that both men fought bitterly to attain. Obama and McCain clashed repeatedly on the campaign trail over foreign and domestic policy in sometimes heated exchanges that occasionally veered into the personal. But Obama made clear that period had passed even as he predicted the two would not always get along in the future. "John is not known to bite his tongue and if I'm screwing up, he's going to...