another pass at the summary

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/rprotobuf@841 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
a missing dot

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/rprotobuf@842 edb9625f-4e0d-4859-8d74-9fd3b1da38cb