included the energy fluxes transported by the diffusive component fluxes
times the enthalpy of the components
applies only for the free flow region

reviewed by Bernd and Vishal


git-svn-id: svn://svn.iws.uni-stuttgart.de/DUMUX/dumux/trunk@13165 2fb0f335-1f38-0410-981e-8018bf24f1b0