Mercury News: Congress moved the nation toward a smarter, greener future by voting last week to raise auto mileage standards for the first time in more than 30 years. But it dropped numerous renewable energy measures to ensure passage of an overall energy bill this year. Lawmakers next year should revisit a key policy left on the cutting-room floor: extending and improving tax incentives for installing solar energy. Congress should pass the solar tax credits, either on their own or as part of …