Dropping support for MPI 2.0

We are considering dropping support for MPI 2.0 in the 1.14.4 release, and we would appreciate the user community’s feedback on the implications of this decision. In reality, we have not tested HDF5 with MPI 2.0 since version 12.1, and while we have fixed some build issues in the latest 1.14.3 release, some tests still fail. Rather than spending resources on improving the current MPI 2.0 issues and adding it to testing, we believe it’s better to require the minimum MPI 3.0 standard, officially.