velocities should be of precision Scalar and not the one of the grid. This...

velocities should be of precision Scalar and not the one of the grid. This makes it possible to use quad in stead of double precision. 
(dunecontrol with  --enable-quad and 
SET_TYPE_PROP(CombustionProblem, Scalar, double ); // quad / double  )

reviewed by Bernd

git-svn-id: svn://svn.iws.uni-stuttgart.de/DUMUX/dumux/trunk@11971 2fb0f335-1f38-0410-981e-8018bf24f1b0