Zoltan2: Use MPI_Alltoallv for all-to-all, instead of hand-rolling it from sends and receives
Created by: mhoemmen
@trilinos/zoltan2
See Trilinos/packages/zoltan2/src/util/Zoltan2_AlltoAll.[ch]pp
. If necessary, add a Teuchos wrapper for MPI_Alltoallv
.