WASHINGTON (Reuters) - The five-year-old U.S. housing boom is likely to slow in 2003 and could dampen consumer spending, which has been fueled by the thriving housing market, Federal Reserve Chairman Alan Greenspan said on Tuesday in comments that rattled housing markets. "With home price increases now subsiding, and mortgage interest rates no longer declining at last year's impressive pace, some slowdown in the rate of mortgage debt expansion is to be expected," he told a conference of the Independent Community Bankers of America in Orlando, Fla., via satellite. Shares of homebuilder stocks tumbled as the Fed chairman, while ruling...