Defstruct copiers and included structures

[Rob MacLachlan <RAM@CMU-CS-C.ARPA>]

Query: Does a copier for a structure correctly copy all structures
       which include that structure?

    I would argue that it should, both on esthetic and practical
grounds.  Since the including structure is a subtype of the included
structure, it should inherit all operations on that structure.  It
would also be useful to be able count on this behavior.  It turns out
that our implementation already does this, since it uses the same
copier function for all structures.

  Rob