remove R < 2.12.1 tweaks

git-svn-id: svn+ssh://svn.r-forge.r-project.org/svnroot/vegan/pkg/vegan@2598 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
remove tweak against changed cmdscale output in R 2.13.0 (depend on newer R)

git-svn-id: svn+ssh://svn.r-forge.r-project.org/svnroot/vegan/pkg/vegan@2599 edb9625f-4e0d-4859-8d74-9fd3b1da38cb