The US coast guard is staging a huge exercise in Florida in preparation for a possible mass exodus from Cuba in the event of the death of Fidel Castro.More than 300 agents and 85 law enforcement agencies are taking part in the two-day Operation Vigilant Sentry. Actors are playing imaginary Cuban migrants in mock interceptions. The operation has taken on a renewed urgency since President Castro fell ill and handed temporary power to his brother Raul last July. President Castro recently spoke in a live broadcast with his Venezuelan counterpart Hugo Chavez, but has not been seen in public...