Chen Xiuzhen, right, and a relative, Xi Yunzhen, washed at a refugee relief center in Yuejin, where tight quarters offered little privacy. HOWARD W. FRENCHPublished: May 25, 2008CHENGDU, China — The secretary general of the United Nations, Ban Ki-Moon, flew to the heart of China’s earthquake zone in Sichuan Province on Saturday to praise the nation’s response to the disaster and pledge his organization’s support.Mr. Ban met in Yingxiu, one of the towns hardest hit by the earthquake, with the Chi