update NEWS for new GC related features.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47536 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
update NEWS for frozen nil/true/false.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47537 b2dd03c8-39d4-4d8f-98ff-823fe69b080e