Sell your house right now and buy some art: that's Londonist's advice for beating the credit crunch. At least, that's the only conclusion to draw on hearing that Christie's have had a second record-breaking art sale inside of a week. This one saw a new world record set for a Jeff Koons sculpture – £12.9 million for his 'Ballon FLower, Magenta', a huge chrome sculpture that has stood on display in St James's Square......