WASHINGTON – U.S. single-family homebuilding increased in April, but data for the prior month was revised sharply lower, suggesting that the housing market slump was far from over even as some segments show signs of stabilizing. The rise in single-family housing starts last month reported by the Commerce Department on Wednesday was concentrated in the West, with the rest of the three regions reporting big declines. Shortages of some materials were likely hampering builders, with the homebuilding backlog surging and completions declining. Single-family housing starts, which account for the bulk of homebuilding, rose 1.6% to a seasonally adjusted annual rate of 846,000 units last month. Data for March was revised down to show single-family homebuilding falling to a rate of 833,000 units instead of increasing to a pace of 861,000 units as previously reported. …But single-family building permits rose 3.1% to a rate of 855,000 units in April, the highest level since last September.