People light candles during a night vigil at Nyanza Genocide Memorial Center, Kigali, Rwanda. This month Rwanda is paying tribute to the victims of genocide 30 years after a vicious campaign orchestrated by Hutu extremists tore the country apart. Photograph: Guillem Sartorio/AFP/Getty It took me a moment to realise that the airline staff at the gate in front of me were shaking their heads. It was March 25th, and I was in Addis Ababa airport in Ethiopia, about to board a flight to Kigali, the capital of Rwanda. Or not. I would not be allowed any further, the staff were...