Two issues with mpi communicator configuration

[garrison]

From #21:

Two related issues found while investigating, not addressed here:

• h_comm_size is writable on both config objects, but tpb::diag / gdb::diag
  recompute it from mpi_size, so setting it has no effect.
• gdb_diag's docstring says b_comm_size must be 1, which is enforced nowhere and
  unexplained. If true it deserves a reason; if stale it blocks the one dimension that
  would parallelise the determinant list.

[hfwen0502]

Jim Garrison (@garrison) agree. h_comm_size will be removed from the wrapper layer.

The GDB case needs a lot of more work. There are a lot of changes in the sbd upstream and we would need to use the new APIs in order to lift the b_comm_size=1 constraint. Kevin J. Sung (@kevinsung): Will you have time to work on this? Or you would prefer me to look into it?

[kevinsung]

Jim Garrison (@garrison) agree. h_comm_size will be removed from the wrapper layer.

The GDB case needs a lot of more work. There are a lot of changes in the sbd upstream and we would need to use the new APIs in order to lift the b_comm_size=1 constraint. Kevin J. Sung (@kevinsung): Will you have time to work on this? Or you would prefer me to look into it?

I won't have time to look into this soon, so It would be great if you could.