Nikkei posts biggest gain since June 2013; Abenomics in focus as ministers quit

* News GPIF raising stock allocation to 25 pct underpins sentiment * Resignation of two cabinet members a big blow to Abe - analyst By Ayai Tomisawa TOKYO, Oct 20 (Reuters) - Japan's Nikkei share average surged 4.0 percent on Monday to post its biggest daily rise since June 2013 as investors took heart from upbeat U.S. data and the weaker yen lifted exporters such as Toyota Motor Corp and Honda Motor Co. Also underpinning the market was news that Japan's $1.2 trillion public pe