By Dan Whitcomb LOS ANGELES (Reuters) - An autopsy was conducted on Monday on the body of the adult son of popular evangelical pastor Rick Warren, who was found dead on Friday with a gunshot wound, California coroner's officials said on Monday. Rick Warren said in a letter to staff of his Orange County-based Saddleback Valley Community Church that Matthew Warren, 27, committed suicide after a lifelong struggle with depression and mental illness. ...