McClatchy: Secretary of State Hillary Clinton Saturday set a new tone for U.S. relations with China, saying the two nations would join a common battle against global warming even as they look for ways to pull the world out of economic turmoil and recession. Clinton cited the “tremendous opportunity” before Washington and Beijing as they unite on “one of the most important issues that has ever, ever faced humanity.” After touring an energy-efficient, low-polluting power generating plant …