AMSTERDAM/CAPE TOWN, May 25 (Reuters) – A Rwandan man accused of ordering the killing of some 2,000 Tutsis who were seeking refuge in a church during the 1994 genocide has been arrested in South Africa, a U.N. war crimes tribunal and South African police said on Thursday. Former police officer Fulgence Kayishema had been on the run since 2001, when the International Criminal Tribunal for Rwanda…