By Rosa Tania Valdes HAVANA (Reuters) – The Colombian government and left-wing FARC rebels ended a 14th round of peace negotiations on Thursday saying they had made progress on part of a six-point agenda, even as they accused each other of violating the principles underlying the talks. A joint statement said the parties "continue advancing in developing and writing up accords … around the second point of the agenda on political participation," including rights and guarantees for the exercise of political opposition. …