preparing support for pick-n scoring; added distractor analysis to show() method

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/klausur@106 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
pick-n seems to work

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/klausur@107 edb9625f-4e0d-4859-8d74-9fd3b1da38cb