Redefining structure accessors (summary)

Let's see if I can summarize the discussion.

Attempts to redefine structure accessors should be a cerror.  If you
continue, then the structure is undefined (mostly) and the function is
created.  This seems better than the current behavior of just warning
you about it and undefining the structure anyway.

(compile accessor new-def) should also be a cerror.

(setf (fdefinition accessor) new-def) shouldn't do anything special.

The structure printer and inspector should be modified to use
%instance-ref so that we can still print and inspect structures even if
the accessor has been redefined.

How does that sound?

Ray