experimental method = "F" for mixed (without p-values)

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/afe@102 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
renamed colname stat to F in output of mixed()

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/afe@103 edb9625f-4e0d-4859-8d74-9fd3b1da38cb