add uneven plots unit test in allPerms

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/vegan@2845 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
simplify code, remove redundant lines.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/vegan@2846 edb9625f-4e0d-4859-8d74-9fd3b1da38cb