The HDF5 library was made thread-safe via excessive locking, so does
not gain much from reads being parallelized.
By using the H5DOread_chunk function (introduced in HDF5 1.10.2)
we reduce the time spent the library, improving performance for
when XDS uses multiple threads to process data.
The decompression and type conversions have to be done manually
however, and this is only used in a limited case.
Charles Mita
ace6a46717