Detroit Free Press: President Barack Obama and environmentally conscious lawmakers in both parties are trying to harness the torrent of stimulus cash unleashed by Congress to sensible long-term policies, especially in the realm of energy conservation. One of the brightest prospects for such a hitch-up is offering cash vouchers to motorists who trade their old vehicles for new, more fuel-efficient ones. Congressional Democrats seem likely to authorize such an incentive, but first they’ll have to pluck the …