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

> 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.

Yes, define-datatype/contract was something I had originally wanted, but 
Robby has convinced me that this is somewhat of an abuse of the contract 
system. Contracts are really only meant to be used at module boundaries, 
and define/contract is probably something to be avoided in general.

Dave