MPI_STATUS_IGNORE informs MPI to not fill an MPI_Status, 
which saves some time. It is used in message reception (MPI_Recv), 
non-blocking operations wait (MPI_Wait, MPI_Waitany) and test 
(MPI_Test, MPI_Testany). A version of MPI_STATUS_IGNORE exists also 
for arrays of statuses: MPI_STATUSES_IGNORE.