Add svn:keywords property to headers in public path so $Date$ etc.
always get expanded.


git-svn-id: https://cvs.khronos.org/svn/repos/ogl/trunk/doc/registry/public/api@23649 e7fa87d3-cd2b-0410-9028-fcbf551c1848


git-svn-id: https://cvs.khronos.org/svn/repos/ogl/trunk/doc/registry/public/api@23652 e7fa87d3-cd2b-0410-9028-fcbf551c1848