define 'strata' via plots in permutations

git-svn-id: svn+ssh://svn.r-forge.r-project.org/svnroot/vegan/pkg/vegan@2658 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
revert r2658: tried to fix an issue that was fixed already in r2655 in permute

git-svn-id: svn+ssh://svn.r-forge.r-project.org/svnroot/vegan/pkg/vegan@2659 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
fix plotting renyiaccum when only one index was used

git-svn-id: svn+ssh://svn.r-forge.r-project.org/svnroot/vegan/pkg/vegan@2678 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
renyiaccum gained a collector curve to be used with summary of permutations

git-svn-id: svn+ssh://svn.r-forge.r-project.org/svnroot/vegan/pkg/vegan@2679 edb9625f-4e0d-4859-8d74-9fd3b1da38cb