[Mpi3-hybridpm] MPI_Comm_split_type

Attached is the updated context chapter with the new MPI_Comm_split_type function (marked in red). Please look through it to make sure we didn't miss anything. For the official reading, we'll drop the MPI_COMM_TYPE_PROCESS constant; the endpoints proposal will add it back. -- Pavan -- Pavan Balaji http://www.mcs.anl.gov/~balaji