Experts Predict African Food Crisis     A group in Washington has released a study that says Africans probably will not have enough food to eat 20 years from now. An International Food Policy Research Institute report says African governments must invest in programs to increase water for farming. It also says programs for crop research and improved are needed by the year 2020. The report says one-third of African children currently suffer from hunger. It says the number could become as high as 49 percent by the year 2020. The report was based on a computer study of population, prices, and production of 16 kinds of goods.