Merge pull request #668 in HDFFV/hdf5 from ~BYRN/hdf5_adb:develop to develop
* commit '75e6579cf232e6c2a8f8c0519a67801fd5dd1f7b':
Restore GEN_HDRS and remove cache sets for defaults
Test program generation should default off
Generate headers for 1.10 should default off
