A new Hollywood movie is raising tough questions about Africa's bloody diamond trade. Sahr Amara is stooped low, knee-deep in a muddy river, in the fifth hour of his workday. As he has each day for the past week, the 18-year-old will earn a stipend of only 7 cents, enough to buy himself a bowl of porridge to see him through the day. "If I find a big diamond, I can afford to go to school, I can learn, and then I can help my family and even my village," he says. So far the plan has proved elusive; he has found no gems during his first week of work. "It's not easy," he says. "I