(This is the Warren Buffett Watch newsletter, news and analysis on all things Warren Buffett and Berkshire Hathaway. You can sign up here to receive it every Friday evening in your inbox.) Berkshire Hathaway CEO Greg Abel is now a citizen of the United States. Abel, a longtime Iowa resident who was born in the Canadian city of Edmonton in 1962, was among the roughly two dozen people from 16 countries who participated in an annual naturalization ceremony hosted by the Iowa Cubs Thursday night in