NEW YORK (Reuters) - Former Federal Reserve Chairman Alan Greenspan said on Thursday that the "extraordinary" boom in the U.S. housing market in recent years is over. "This has been quite an extraordinary boom," Greenspan told a Bond Market Association dinner in New York. "The boom is over. I think we can safely say that with a strong degree of confidence." Greenspan said there was a "high degree of froth in the system," and that it was clear that home equity extraction and the turnover of home sales was waning.