SACRAMENTO, California (Reuters) - California Gov. Arnold Schwarzenegger signed an executive order on Thursday to reduce carbon emissions from transportation fuels, a move intended to widen the development and use of alternative vehicle fuels in the nation's biggest state. The order, the first of its kind in the United States, sets a standard to cut carbon levels in vehicle fuels by at least 10 percent by 2020. It also will implement a state law adopted last summer that mandates state emissions caps to reduce greenhouse gases linked to global warming by 25 percent by 2020. In a signing ceremony outside...