niche library

Hi,

The niche (netCDF interface covering HDF encoding) library is much less
space-inefficient than my last note would indicate.  I had just looked at
the files produced by nctest, which are unrealistically small, so the extra
metadata overhead for HDF swamped the data sizes and made it appear that the
HDF representation takes significantly more space than the XDR
representation.  In fact the differences are small for realistic files that
are mostly data.  For example, here's the sizes of one of our decoded NPS
GRIB files of relative humidity data at 6 levels and 8 forecast times on a
33 by 36 lat-lon grid:

       241327 r.hdf
       230032 r.cdf

Drawing conclusions from timing nctest was also unrealistic.  I will post
some more realistic timing benchmarks later.

--Russ