vchoi_fork

Merge pull request #2822 in HDFFV/hdf5 from hdf5_1_12_coll_chunk_fill_fix to hdf5_1_12

* commit '3e4f255c5031f14a68d387df0762f7a2210df5a3':
  Added release note for MPI type fix
  Simplify default use of MPI_BYTE
  Don't free builtin MPI_BYTE MPI type
  Simplify code to avoid using a boolean to free MPI types
  Avoid creating MPI datatypes on ranks with 0 chunks to write'