update of reference solutions of 3p3c box and forchheimer2p

the reference solutions were not valid any more after commit 12215:
removal of incremental update of average molar mass ind fluidstate. 
It is unclear why this led to changing reference solutions, but no
substantial difference in results, also after longer simulation runs,
could be observed. 



git-svn-id: svn://svn.iws.uni-stuttgart.de/DUMUX/dumux/trunk@12584 2fb0f335-1f38-0410-981e-8018bf24f1b0