- Cross-validation was potentially wrong for CoxPH() models.
  Users can now choose if they want the naive cross-validation
  or the improved version by Verweij and van Houwelingen (1993);
  (spotted by Holger Reulen)

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/mboost@806 edb9625f-4e0d-4859-8d74-9fd3b1da38cb