"proxy" data objects in visad.data.netcdf.in

Hi,

I've added support for "proxy" data objects to the visad.data.netcdf.in
subpackage.  Such data object utilize visad.FileFlatField wherever
appropriate.

It's pretty cool.  :-)

One question, though.  Where should the decision to use FileFlatFields
be made?  In the Form's?  In the Repository?  By the user?  The
java.lang.Runtime.getMemoryAdvice() method, which indicates the level of
memory usage, might be applicable.

--Steve