change from MPI_COMM_WORLD to custom mpiCommWorld. needs further testing...

[3gx]

First attempt to remove MPI_COMM_WORLD from Bonsai in favour of a custom mpiCommWorld communicator.

Todo:

• Split communicator n-ways when >1 ranks per nodes are found consistently for all jobs, so that we can n subcommunicators with 1 rank per node.
• tests, tests, tests

Not yet for merging, but to track the changes..

[3gx]

Occurrence of MPI_COMM_WORLD in *.h:

./Bonsai$ find . -iname '*.h' |xargs grep -Hn MPI_COMM_WORLD
./IceT-2-1-1/tests/mpi_comm.h:21:    comm = icetCreateMPICommunicator(MPI_COMM_WORLD);

Occurrence of MPI_COMM_WORLD in *.cpp:

./Bonsai$ find . -iname '*.cpp' |xargs grep -Hn MPI_COMM_WORLD
./runtime/src/bonsai_io.cpp:219:  MPI_Comm comm = MPI_COMM_WORLD;
./runtime/src/main.cpp:953:  //  const char * tempRankStr = getenv("OMPI_COMM_WORLD_RANK");
./runtime/src/main.cpp:992:  const MPI_Comm &mpiCommWorld = MPI_COMM_WORLD;
./tools/parallelIO/write_test.cpp:36:  MPI_Comm_rank (MPI_COMM_WORLD, &rank); 
./tools/parallelIO/write_test.cpp:37:  MPI_Comm_size (MPI_COMM_WORLD, &nrank);
./tools/parallelIO/write_test.cpp:39:  const MPI_Comm MPI_WORKING_WORLD = MPI_COMM_WORLD;
./tools/readSnap/read_tipsy.cpp:9:  MPI_Comm comm = MPI_COMM_WORLD;
./tools/cvt2grid/cvt2grid.cpp:89:  MPI_Comm comm = MPI_COMM_WORLD;
./tools/cvt2grid/cvt2gridTree.cpp:89:  MPI_Comm comm = MPI_COMM_WORLD;
./tools/cvt2grid/densCalc.cpp:134:  MPI_Comm comm = MPI_COMM_WORLD;
./tools/IO/benchmark.cpp:8:  MPI_Comm comm = MPI_COMM_WORLD;
./tools/IO/cvt_tipsy2bonsai.cpp:102:  MPI_Comm comm = MPI_COMM_WORLD;
./tools/IO/readBonsai.cpp:80:  MPI_Comm comm = MPI_COMM_WORLD;
./tools/bonsaiRenderer/density/renderer_with_test.cpp:1331:  MPI_Bcast(this, sizeof(SmokeRendererParams),  MPI_BYTE, 0, MPI_COMM_WORLD);
./tools/bonsaiRenderer/density/renderer.cpp:1369:  MPI_Bcast(this, sizeof(SmokeRendererParams),      MPI_BYTE, 0, MPI_COMM_WORLD);
./tools/bonsaiRenderer/density/renderloop.cpp:1029:      MPI_Bcast(cameraTemp, 7, MPI_FLOAT, 0, MPI_COMM_WORLD);
./tools/bonsaiRenderer/main.cpp:529:  MPI_Comm comm = MPI_COMM_WORLD;
./tools/bonsaiRenderer/main.cpp:603:  IceTCommunicator icetComm = icetCreateMPICommunicator(MPI_COMM_WORLD);

[jbedorf]

These changes worked on PD, merging them to allow wider testing.