Mon Jan 9 20:46:20 EST 2012

replace stx by r s ?

Maybe that's a better approach, since only Code needs this, and Code
knows how to unpack a singly wrapped Term.  Also the symmetry between
(r s) and sr as that in Struct is obvious.  stx looks a bit like a hack..

However, ths messes up StructVarCons, but it that still needed?  It
seems StructRepr is enough..

EDIT: Actually, that was quite straightforward.

There are some more simplifications.  structVar doesn't need to return
both r s and sr: the StructRepr class is available so only sr or r s
is enough.

Did that + implemented stub for variable reuse.