hdf5_msb

Merge pull request #765 in HDFFV/hdf5 from bigio_test_refactoring to hdf5_1_10

* commit 'b829979c7047070bb92d67e5a5374c093319bab3':
  Follow up on editing suggestions by Scot
  Refactored testpar/t_bigio.c and then added a basic description of these test changes into RELEASE.txt (HDFFV-10301)