message: Add MPI_C_COMPILER, MPI_CXX_COMPILER
diff: # MPI - manually added for now.
  ##############################################################################
  set(ENABLE_MPI ON CACHE PATH "")
  -set(MPI_C_COMPILER "/usr/local/tools/mvapich2-gnu-2.0/bin/mpicc" CACHE PATH "")
  -set(MPI_CXX_COMPILER "/usr/local/tools/mvapich2-gnu-2.0/bin/mpicxx" CACHE PATH "")
  -set(MPI_Fortran_COMPILER "/usr/local/tools/mvapich2-gnu-2.0/bin/mpif90" CACHE PATH "")
  +set(MPI_C_COMPILER "/usr/global/tools/clang/chaos_5_x86_64_ib/clang-omp-3.5.0/bin/mpiclang" CACHE PATH "")
  +set(MPI_CXX_COMPILER "/usr/global/tools/clang/chaos_5_x86_64_ib/clang-omp-3.5.0/bin/mpiclang++" CACHE PATH "")
  set(MPIEXEC "/usr/bin/srun" CACHE PATH "")
  set(MPIEXEC_NUMPROC_FLAG "-n" CACHE PATH "")
  