fix ompi_request_wait vs ompi_request_wait_all and
MPI_STATUS_IGNORE vs MPI_STATUSES_IGNORE

This is a back-port of commit open-mpi/ompi@64c18686b7b20503519042fe0edbe0ca5f2e904a
Merge pull request #72 from ggouaillardet/topic/ompi_request_wait_fixes

fix ompi_request_wait vs ompi_request_wait_all