string.c: new string for fake string
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@51355 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
string.c: new string for fake string
string, and pool shared target unless substring.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@51355 b2dd03c8-39d4-4d8f-98ff-823fe69b080e