regularized Brooks-Corey: regularize krw for Sw > 1 instead of > 0

Grr something like this happens too often, we need unit tests!

git-svn-id: svn://svn.iws.uni-stuttgart.de/DUMUX/dumux/trunk@4319 2fb0f335-1f38-0410-981e-8018bf24f1b0