Significant milestone for netCDF-4/HDF5


Ed just reported that he got his netCDF-3 C interface that uses the
HDF5 API and storage layer to pass the current netCDF comprehensive
test suite.  This uses an unmodified HDF5 1.6.1 library and a
basically unmodified nc_test from the latest netCDF 3.5 release.

Ed's implementation demonstrates that the current HDF5 even without
enhancements is adequate for a correct implementation of netCDF-3 and
that the backward-compatibility approach is sound, since the new
library can use the old interface and can access data from either
current netCDF-3 or new HDF5 files transparently by just recompiling
and relinking old netCDF-3 programs.  We weren't sure this level of
both API and format compatibility could be achieved, but now we know
it's practical.

I think this puts us ahead of schedule, providing a baseline
implementation we can later compare with a tuned version that uses an
enhanced HDF5 library.

Now that the netcdf-3 tests pass, we can start to investigate and
write tests for some of the new functionality that this gives us with
very little additional work, such as large files and new data types.

We can also begin planning improvements to both the current prototype
and the HDF5 implementation to serve as a basis for the netCDF-4
enhancements we have in mind.  We could also look at performance,
taking care to avoid premature optimizations until we understand how
to make the changes needed to support the netCDF-4 enhancements.

Thanks to Ed, Quincey, and others who have been involved in helping to
achieve this significant milestone!