A study published by the International Monetary Fund (IMF) finds that eight of the 12 fastest-growing economies in Africa in recent years did not rely on natural resources. Together these economies grew more quickly even than the group of oil producers.     The climate for private business is also much improved. Price controls and state-backed monopolies have been swept away. Rwanda stands out for its progress. Its coffee farmers once had little incentive to produce for export. The state set a single price for beans and took the lion’s share of any profits. But from the mid-1990s it granted private enterprise a bigger role. Now gourmet coffee from Rwanda is sold in posh grocery stores around the world.       Free exchange