DAWIT ENDESHAW  THOUSANDS of people from the Oromo, Ethiopia's largest ethnic group, have celebrated their thanksgiving festival in Bishoftu city amid tight security after the authorities said they had seized weapons and foiled attacks in previous days. The Irreecha festival has been the scene of violent protests before by the Oromo, who have long complained of political exclusion. Recent unrest, including the killing of a popular singer in June and the arrest of prominent Oromo politicians, heightened concern of violence at the two-day festival. On the eve of the festival, forces from both regional and federal police, as well from…