Internal bench() works again

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/datatable@1157 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
global variables=NULL to keep R CMD quiet for internal bench()

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/datatable@1158 edb9625f-4e0d-4859-8d74-9fd3b1da38cb