date_core.c: more write-barriers
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47734 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
date_core.c: more write-barriers
VALUE members to find out missing write-barriers.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47734 b2dd03c8-39d4-4d8f-98ff-823fe69b080e