small changes in octav and rad and their plot methods to avoid odd results (like unordered values and abundances <0

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/sads@188 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
small corrections on rad.R and vignette

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/sads@189 edb9625f-4e0d-4859-8d74-9fd3b1da38cb