two things changed in all fluidsystems:

- enthalpy of gaseous mixture is composed of the (mass fraction 
  weighted) enthalpies of the pure components (at temperature and 
pressure of the phase)
- enthalpy of the liquid mixture is only composed of pure main component
  (we need to
  look up enthalpies of solution to improve this)


git-svn-id: svn://svn.iws.uni-stuttgart.de/DUMUX/dumux/trunk@6722 2fb0f335-1f38-0410-981e-8018bf24f1b0