ANOVA now gives warning for empty cells

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/afe@132 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
git-svn-id: svn://svn.r-forge.r-project.org/svnroot/afe@133 edb9625f-4e0d-4859-8d74-9fd3b1da38cb