[plt-scheme] super-structs and structure type descriptors

Thanks for the explanation.  I'm going with Robby's solution, as it turns out 
that I need the data-
structures I was dealing with in multiple modules.

I know about your PLaneT package.  In fact, I'm using it right now.  I wanted 
to write a `define-datatype/
contract' macro, and `define-struct/contract' was to be an auxillary to that.  
Well, it seems as though I 
don't want that anymore.

-Arjun