Bloomberg: Requiring California utilities to get half their power from renewable sources by 2025 should be an easy sell in the ecology-conscious state, home to one of the world’s strictest laws to fight global warming. Yet voters may reject the Nov. 4 ballot measure, known as Proposition 7, amid opposition from an unusual alliance of Democrats, Republicans, environmental groups, utilities and renewable-energy companies. Environmentalists say the plan contains loopholes that would make it …