change to instance structure protocol

[Jon L White <jonl@lucid.com>]

[This looks like an excellent use of the somewhat nascent ability to make
new (effective) SLOT-DEFINITION classes.]

I'd be a bit concerned about slowdown in regular (non-inlined) SLOT-VALUE
because of it -- whereas now a SLOT-VALUE has to do a CLASS-OF, followed 
by some kind of table lookup, it will (under this proposal) have to do
an additional lookup of the named SLOT-DEFINITION object from the class 
object.  I don't suppose this is a critical flaw, but just one more thing 
to worry about.

There's no doubt, whatsoever, in my mind that the goal you are striving
for in this proposal is critical.  The several papers at OOPSLA show
precisely this need.



-- JonL --