hdf5

Reduce differences between my -Werror branch and `develop`:

Rename index -> idx, fileno -> fnumber, fileno -> fno to avoid GCC
shadowed declaration warnings about index(3).

Convert #pragma GCC diagnostic push/pop/ignored to the HDF5 library's
H5_GCC_DIAG_OFF()/H5_GCC_DIAG_ON() macros.