mixed() gives warning if nested model provides worse fit (logLik) than full model.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/afe@118 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
added set.data.arg argument to mixed()

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/afe@119 edb9625f-4e0d-4859-8d74-9fd3b1da38cb