Merge pull request #812 in HDFFV/hdf5 from ~LRKNOX/hdf5_lrk:hdf5_1_8 to hdf5_1_8
* commit '2c3bde7f7448d2b41c953ffe4a32a9456ada2a5b':
Add assignment to get value from environment variable realtimeOutput. Propagate changes to Makefile.ins with bin/reconfigure.
Add HDF5 1.8.20 RELEASE.txt file to HISTORY-1_8.txt. Removed new features and bug fixes released in HDF5 1.8.20 from RELEASE.txt. Copied Platforms Tested, Tested Configuration Features Summary, More Tested Platforms, and Known Problems sections from 1.8.20 RELEASE.txt to hdf5_1_8 RELEASE.txt.
