message: better error message when the mpi device cannot be created in ospInit()
diff: @@ -61,8 +61,15 @@ inline ospray::api::Device *createMpiDevice()
  try {
  device = ospray::api::Device::createDevice("mpi");
  } catch (const std::runtime_error &) {
  + try {
  ospLoadModule("mpi");
  device = ospray::api::Device::createDevice("mpi");
  + } catch (const std::runtime_error &) {
  + std::string error_msg = "Cannot create a device of type 'mpi'! Make sure "
  + "you have enabled the OSPRAY_MODULE_MPI CMake "
  + "variable in your build of OSPRay.";
  + throw std::runtime_error(error_msg);
  + }
  }
  return device;
  