On the '1.8.x-r1643074' branch: To avoid a swig-rb bindings failure,^Mdefine a private constant in a different way.

git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/1.8.x-r1643074@1644474 13f79535-47bb-0310-9956-ffa450edef68