Fix Jira issue NCF-29 (https://bugtracking.unidata.ucar.edu/browse/NCF-29):
making the netCDF-4 library ignore HDF5 datasets and attributes which have
datatypes (such as references) that it doesn't understand.
Tested on:
Mac OSX/64 10.8.2 (amazon) w/--enable-netcdf-4 --enable-extra-tests --enable-extra-example-tests
--disable-shared --enable-logging