1. Modified Netcdfdataset.opendap4byreflection to invoke a
   factory class for DAP4; also xpanded exception catching
   in that code.
2. Apparently one of my changes got lost.
   So, in Nc4Iosp.readOpaque: the code
   is not getting the proper shape;
   it is treating all opaque variables
   as having rank==1.