Merge branch 'master' into r-forge-svn-local

Add permustats() function and their support with replace and
enhance old density and densityplot methods for permutation
and simulation results.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/vegan@2889 edb9625f-4e0d-4859-8d74-9fd3b1da38cb