Check for valid mode


git-svn-id: svn://svn.r-forge.r-project.org/svnroot/tm@1298 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Use setNames() instead of structure(..., names)

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/tm@1299 edb9625f-4e0d-4859-8d74-9fd3b1da38cb