[Dune] MPI Handling in dgfparser

[Christian Engwer]

Hi,

> I wrote an example implenmentation of an MPIHelper last weekend.

Great :-)

> Of course this is only a first step. To be fully generic one would
> have to add Wrappers to the actual mpi methods like it is already done
> (partly?) in class CollectiveCommunication (see
> dune/common/mpicollectivecommunication.hh and
> dune/common/collectivecommunication.hh).
> 
> Looking forward to your comments!

As this is an abstraction for the communication I would suggest to use
a different name. The whole communication is not limited to mpi, so
that we might as well choose a name like Dune::ParallelEnvironment.

I think this is great starting point and can replace define hacks like
the MPISTART and MPIEND. But I'm not shure what to do with the
communiator itself... If you want to support all the communicator
reorganization methods the interface will get quite big. Also we have
to destiguish between the setup of the parallel environment and the
communication. The communication can not be handled by a singleton
class, but must be done via something like the CollectiveCommunication
class which can be instantiated with a specific MPI_Comm object.

Christian