SACRAMENTO, California (Reuters) - The federal government will spend $2 billion to extend a subway line under Los Angeles' storied Wilshire Boulevard, an effort to ease congestion in one of the country's most transited corridors and to eventually link downtown to the beach with a "Subway to the Sea." The project is meant to improve traffic in a part of the city where it can take hours to go just a few miles, with train stations to be built at major cultural attractions, including museums and the glitzy shopping areas of Beverly Hills. Backers hope at some point to expand...