model = 'asymp' did not fit SSasymp but SSlogis (like model = 'logis', too)

git-svn-id: svn+ssh://svn.r-forge.r-project.org/svnroot/vegan/pkg/vegan@2462 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Merge branch 'r-forge-svn-local'