By Jonathan Stempel (Reuters) -Berkshire Hathaway signaled on Saturday that it remained cautious about markets, letting cash swell to a record $381.7 billion even as profit rose, in its last financial report before Warren Buffett bows out as chief executive. For a 12th straight quarter, Buffett's conglomerate sold more stocks than it bought for its$283.2 billion equity portfolio, whose holdings include Apple and American Express. Berkshire also did not repurchase any of its own stock, the fifth straigh ...