[3p3c]

- changed naming of mole fractions x^alpha_kappa to x^kappa_alpha
- added zeroThreshold for the kuevette problem, because the non-wetting
  phase already disappaered at the end of the simulation

reviewed by timok



git-svn-id: svn://svn.iws.uni-stuttgart.de/DUMUX/dumux/trunk@15436 2fb0f335-1f38-0410-981e-8018bf24f1b0