h5py and hdf5-mpi

[Drew Parsons <dparsons@debian.org>]

We need to change h5py to support hdf5-mpi.  h5py is somewhat crippled 
as serial-only.

We could just do it straight away in python3-h5py.  Is there much point 
having h5py support both hdf5-serial and hdf5-mpi?  Perhaps there is, in 
which case we need to set up multiple builds and use alternatives to set 
the preferred h5py.

A related question, is there much point setting up support for 
hdf5-mpich as well as hdf5-openmpi?  Increasing build and 
package-alternatives complexity, but once it's done once to distinguish 
hdf5-serial from hdf5-mpi, it's not that much more work to also split 
hdf5-mpi between hdf5-mpich and hdf5-openmpi.

Drew