the new stokes2c problem now uses the stokesnc model since stokes2c is...

the new stokes2c problem now uses the stokesnc model since stokes2c is deprecated/obsolete. new reference test file was necessary due to more output data of stokesnc and small numerical differences in the order of 10^-8 for some entries.

git-svn-id: svn://svn.iws.uni-stuttgart.de/DUMUX/dumux/trunk@12095 2fb0f335-1f38-0410-981e-8018bf24f1b0