small tweaks to Makefile

remove ephemeral pdf figures
add zip entry to prepare upload to jss


git-svn-id: svn://svn.r-forge.r-project.org/svnroot/rprotobuf@866 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
do not remove article when running clean


git-svn-id: svn://svn.r-forge.r-project.org/svnroot/rprotobuf@867 edb9625f-4e0d-4859-8d74-9fd3b1da38cb