WASHINGTON (Reuters) -Sales of previously owned U.S. homes increased solidly in August as lower mortgage rates pulled buyers back into the market, though a softening labor market could curb further gains. The National Association of Realtors said on Monday pending home sales, based on signed contracts, rebounded 4.0% last month. Economists polled by Reuters had forecast contracts, which become sales after a month or two, rising 0.2%. Contracts increased in the densely populated South, Midwest and West, b ...