commit 12402 (different calculation of phase enthalpies) changed result.

We agreed that the new consideration of partial pressures makes more
sense, therefore the reference is updated. 


git-svn-id: svn://svn.iws.uni-stuttgart.de/DUMUX/dumux/trunk@12583 2fb0f335-1f38-0410-981e-8018bf24f1b0