ared.At a launch by Renaissance in a Johannesburg hotel last month of the book Africa's Economic Revolution, participants heard a prediction that the region's economy will grow from $2 trillion today to $29 trillion by 2050, greater than the output of both the United States and the eurozone.The chic hotel of the book launch is a world away from Sangbulima, a hamlet of 1 000 souls perched on Tass