Nikkei jumps to 7-year high after BOJ shocks by easing further

* Weak yen drives exporter shares higher * Abe may use strong market performance as ammunition to stick to initial tax hike plan - traders By Ayai Tomisawa TOKYO, Oct 31 (Reuters) - Japanese stocks rocketed more than 5 percent to levels before the global financial crisis on Friday, after the Bank of Japan stunned markets by easing policy further in a move prompted by slow inflation after an April tax hike dented economic growth. The central bank decided to increase the pace at w