No boom lasts forever, and in countries like Britain and Australia, the housing market has suddenly turned lower, leading to discussions of how a plunge can be avoided and what will happen if it is not. The American housing market received a scare yesterday, with a report that the pace of new-home sales slipped in November as the median price of a new home fell to the lowest level in a year. But mortgage applications indicate that a rebound has begun, and in any case, prices of new homes can fail to capture price trends for existing homes in areas...