Reuters: A slide in oil prices may be good for consumers battered by the U.S. economic slowdown, but it could pose a challenge for President Barack Obama’s ambitious plan to revolutionize America’s energy use. Obama’s plan — outlined during the campaign last year when oil prices hit a record $147 a barrel — calls for doubling U.S. alternative energy use within three years while easing reliance on foreign oil. (To see a factbox on Obama’s energy proposals, click ID:nN30365069) Oil …