[Dune] MPI Handling in dgfparser

[Andreas Dedner]

Thimo Neubauer wrote:
> 
> How about wrapping the MPI-startup in a helper class? This would allow
> for something as easy to write as the first pattern (and without any
> defines):
> 
>   MPIHelper mpihelper;
> 
>   grid("name", mpihelper::MPI_COMM_WORLD);
>   // or grid("name", mpihelper)
>   

Once you see it, it seems the obvious solution...
One could use the Dummy class to define the default argument, so that
users without mpi do not have to see anything disturbing with
MPI...