Warren Buffet's Dos and Don'ts   Whether you're a homebuyer considering a mortgage, or an executive weighing a takeover, the 85-year old billionaire has advice for anyone looking to live a more rational, financially successful life.  [Excerpted from Investment News] For anyone wondering, “What would Warren Buffett do?” the 85-year-old billionaire has given plenty of advice in his public remarks and in annual letters to Berkshire Hathaway Inc. shareholders. It doesn't matter whether you're a home buyer considering a mortgage, or an executive weighing a takeover; [...]