Associated Press: Last summer, Xu Demin struggled to cut emissions from his coal-fired factories as part of China’s all-out effort to clean the air for the Beijing Olympics. He could have simply waited six months. This spring, overseas demand for his farming and construction machinery plummeted, forcing him to close two plants and lay off 300 workers. The global economic slowdown is helping to accomplish what some in China’s leadership have striven to do for years: rein in the insatiable demand …