SE Asia Stocks-Fall on gloomy economic outlook; Singapore at 3-wk closing low

April 1 (Reuters) - Southeast Asian stock markets fell on Friday as concerns over global economic outlook dented sentiment after S&P cut its credit outlook for China, and on a gloomy survey of Japanese manufacturing. Singapore's Straits Times Index ended 0.8 percent down at its lowest close since March 10, Thailand's SET Index finished 0.5 percent weaker, and the Philippines was down 0.2 percent. "At the moment, there are so many concerns over the major economies, especially China an