Comment out a dup enum message type that causes problems with
libprotobuf-2.5



git-svn-id: svn://svn.r-forge.r-project.org/svnroot/rprotobuf@882 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Document duplicate enum removal from unittest.proto.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/rprotobuf@883 edb9625f-4e0d-4859-8d74-9fd3b1da38cb