hdf5_ep

Merge pull request #2872 in HDFFV/hdf5 from vol_dataset_io_dxpl_fix_1_12 to hdf5_1_12

* commit '9dde542398800763ab6f26e406c304c2b529a375':
  Bug fix to allow pass-through VOL connectors to set DXPL properties (like requesting collective operations) on dataset I/O