Warren Buffett tumbles to his lowest ever position on the list of the world's richest people after a $2.9 billion charity donation

· Billionaire investor Warren Buffett donated $2.9 billion worth of Class B shares in his Berkshire Hathaway charity this week, taking his total philanthropic contributions to $37 billion in 14 years.
· The donation, however, has pushed him to his lowest ever position on Bloomberg's widely cited Billionaires Index.
· Buffett...