add closest stone features

git-svn-id: svn://svn.code.sf.net/p/fuego/code/trunk@1918 2e953b5c-c64d-0410-be54-f773e93e544c
nakade test cases

git-svn-id: svn://svn.code.sf.net/p/fuego/code/trunk@1919 2e953b5c-c64d-0410-be54-f773e93e544c