MPI 3 deprecates MPI_Type_struct, changes to MPI_Type_create_struct

[bjoo]

I just tried compiling QMP with OpenMPI-4.0 and it complained about MPI_Type_struct, and instructed me to change it to MPI_Type_create_struct instead. It is a straightforward substitution, apparently the function name is all that changes. We should consider changing this as a maintainance, but in a way that we can also keep the old invocation. It only occurs once in lib/mpi/QMP_mem_mpi.c as far as I can tell.

[maddyscientist]

Any reason why this issue isn't fixed yet? As noted above by @bjoo this breaks QMP with OpenMPI 4. MPI_type_create_struct was introduced in MPI-2. I see no reason why the reference to MPI_type_struct can't be expunged.

[bjoo]

I changed the offending MPI_type_struct to MPI_type_create_struct. I also merged master into 'devel' to eliminate that divergence, and then merged the lot into master. If master has undesirable features, I have tagged pre and post merges. Post merge is tagged as qmp2-5-2-rc