Fix a typo and then replace XXX with 300 for now.  This summary looks
pretty good to me, thanks Jeroen and Dirk for greatly improving it.



git-svn-id: svn://svn.r-forge.r-project.org/svnroot/rprotobuf@819 edb9625f-4e0d-4859-8d74-9fd3b1da38cb