WASHINGTON -- Rosemary Kennedy, a sister of John F. Kennedy who was born mentally retarded and lived most of her life in an institution after undergoing a lobotomy, died Friday, her family said. She was 86. Kennedy, the inspiration for the Special Olympics spearheaded by the Kennedy family, had been a patient since 1949 at St. Coletta School for Exceptional Children in Jefferson, Wis. She was the third child and first daughter of Joseph and Rose Kennedy, born a year after her brother became president. In 1941, Joseph Kennedy, worried his daughter's mild mental retardation would lead her into situations...