In yet another chapter in the manic saga of global markets, stocks soared Thursday around the world after European leaders announced yet another comprehensive plan to solve—once and for all?—the deepening sovereign-debt crisis. The outpouring of optimism was given an added boost by the release in the United States of third-quarter economic figures that indicated GDP increased 2.5 percent, and the icing on the proverbial cake was supplied by news that the Chinese government would potentially add some of its trillions in reserves to help shore up ailing European finances.