message: helper: Cast to 'int' explicitly in MPI count arguments
  Without an explicit conversion some compilers warn:
  conversion from 'size_t' to 'int', possible loss of data
  In these cases we do not expect the size to be beyond 2^31.
diff: @@ -184,9 +184,9 @@ void MpiHandshake::Handshake(const std::string &filename, const char mode,
  {
  for (size_t stream = 0; stream < maxStreamsPerApp; ++stream)
  {
  - MPI_Irecv(m_Buffer.data() + PlaceInBuffer(stream, rank), m_ItemSize,
  - MPI_CHAR, rank, rank, MPI_COMM_WORLD,
  - &m_RecvRequests[rank][stream]);
  + MPI_Irecv(m_Buffer.data() + PlaceInBuffer(stream, rank),
  + static_cast<int>(m_ItemSize), MPI_CHAR, rank, rank,
  + MPI_COMM_WORLD, &m_RecvRequests[rank][stream]);
  }
  }
  @@ -204,8 +204,9 @@ void MpiHandshake::Handshake(const std::string &filename, const char mode,
  for (int rank = 0; rank < m_WorldSize; ++rank)
  {
  - MPI_Isend(buffer.data(), m_ItemSize, MPI_CHAR, rank, m_WorldRank,
  - MPI_COMM_WORLD, &m_SendRequests[rank][m_StreamID]);
  + MPI_Isend(buffer.data(), static_cast<int>(m_ItemSize), MPI_CHAR, rank,
  + m_WorldRank, MPI_COMM_WORLD,
  + &m_SendRequests[rank][m_StreamID]);
  }
  // wait and check if required RendezvousAppCount reached
  