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A month ago I visited Kibera, the largest slum in Africa. This suburb of Nairobi, the capital of Kenya, is home to more than one million people, who eke out a living in an area of about one square mile -- roughly 75% the size of New York's Central Park. It is a sea of aluminum and cardboard shacks that forgotten families call home. The idea of a slum conjures up an image of children playing amidst piles of garbage, with no running water and the rank, rife stench of sewage. Kibera...