Nikkei jumps to 7-year high after BOJ's policy shock, GPIF hopes

* Nikkei posts 7.3 pct weekly gain, 1.5 pct monthly gain * Weak yen drives exporter shares higher * Abe may use strong market performance as ammunition to stick to initial tax hike plan - traders * Kuroda taking proactive approach - analysts * Hopes GPIF will announce increase in Japan, foreign stocks help mood By Ayai Tomisawa TOKYO, Oct 31 (Reuters) - Japanese stocks soared to levels before the global financial crisis on Friday, after the Bank of Japan stunned markets