[Warnings] Fix MPI 1 deprecation warnings (by switching to MPI 2).

Intended merge date: 2017-11-17

This fixes warnings of the following form about functions deprecated in MPI 2.

/home/joe/Projekte/dune-simd/dune-istl/dune/istl/paamg/test/parallelamgtest.cc: In function ‘int main(int, char**)’:
/home/joe/Projekte/dune-simd/dune-istl/dune/istl/paamg/test/parallelamgtest.cc:217:3: warning: ‘int MPI_Errhandler_create(void (*)(ompi_communicator_t**, int*, ...), ompi_errhandler_t**)’ is deprecated: MPI_Errhandler_create is superseded by MPI_Comm_create_errhandler in MPI-2.0 [-Wdeprecated-declarations]
   MPI_Errhandler_create(MPI_err_handler, &handler);
   ^~~~~~~~~~~~~~~~~~~~~
In file included from /home/joe/Projekte/dune-simd/dune-common/dune/common/parallel/mpitraits.hh:23:0,
                 from /home/joe/Projekte/dune-simd/dune-common/dune/common/parallel/plocalindex.hh:9,
                 from /home/joe/Projekte/dune-simd/dune-istl/dune/istl/paamg/test/anisotropic.hh:8,
                 from /home/joe/Projekte/dune-simd/dune-istl/dune/istl/paamg/test/parallelamgtest.cc:7:
/usr/lib/x86_64-linux-gnu/openmpi/include/mpi.h:1345:20: note: declared here
 OMPI_DECLSPEC  int MPI_Errhandler_create(MPI_Handler_function *function,
                    ^~~~~~~~~~~~~~~~~~~~~

@all This should make it impossible to compile dune-istl with a version 1 only MPI implementation. I don't know whether it was possible before to use MPI-1, and if so I don't know whether anyone was using MPI-1, but I'd like to give this a chance to be discusses before merging.

Intended merge date: 2017-11-17

changed the description

MPI-1 was explicitly deprecated including a warning. So, merge this for 2.6!

merged

mentioned in commit 32e63b2d

mentioned in commit fe9b6a94

mentioned in merge request !133 (merged)