By Cassandra Garrison and Andrea Shalal MEXICO CITY/WASHINGTON (Reuters) -An outside firm hired to investigate whistleblower allegations found evidence that Inter-American Development Bank President Mauricio Claver-Carone engaged in an intimate relationship with a staffer, three sources briefed on the probe told Reuters. The report also cited examples of abuse of power by Claver-Carone, including his dismissal of some bank employees that investigators believed were in retaliation for various personal conflicts, said the sources, who spoke on condition of anonymity because the process is still …