hdf5

Merging in latest from upstream (HDFFV/hdf5:refs/heads/develop)

* commit 'fb8296371cf45654a9252ed01b635519205da3de':
  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.