- partial revert for 13740de427 (#2158)
MS-MPI does not currently have a MPI_Comm_create_group(),
so keep using MPI_Comm_create() there.
Only affects multi-world simulations.
CONFIG: retain dummy version of libPstream.dll
- retain as libPstream.dll-dummy so that it is available for
manual replacement of the regular libPstream.dll (#2290)
Keep extra copy of libPstream.dll as libPstream.dll-msmpi
(for example) for manual replacement.