Address some reviewer feedback about why we use RObjectTables and some
of the pitfalls, with some of this text provided verbatim from Karl
Millar, who is already thanked in the acknowledgements section.



git-svn-id: svn://svn.r-forge.r-project.org/svnroot/rprotobuf@897 edb9625f-4e0d-4859-8d74-9fd3b1da38cb