Fix subscene bug

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/rgl@1170 79a1b648-8b68-254f-b20b-c0b50f5137bf
name change to arg

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/rgl@1171 79a1b648-8b68-254f-b20b-c0b50f5137bf