hdf5

Merge pull request #1896 in HDFFV/hdf5 from ~DEROBINS/hdf5_der:H5Pset_fapl_mpi to develop

* commit '937616872cf228f838fd1eb2853ce6110f3da10b':
  Minor tweaks to new H5P MPI code based on code review feedback.
  Fixed a bug in the cache image code that was introduced by the HD changes.
  Added H5Pset/get_mpi_params calls and unified them with the MPI-I/O VFD info in H5FDmpio.c.