with-accessors

[Gregor.pa@Xerox.COM]

I presented the current state of CLOS to the people at MCC.  When I got
to with-slots they said "hey thats biased against accessors".  We came
up with the idea of with-accessors which is basically like the long form
of with slots.  

This use of with-accessors:

(with-accessors ((x position-x)
                 (y position-y))
                p1
  (setq x y))

is equivalent to:

(let ((#:g1 p1))
  (setf (position-x #:g1) (position-y #:g1)))

and is parallel to:

(with-slots ((x x)
             (y y))
            p1
  (setq x y))

I think the MCC comment was good and captures a lot of the complaints I
have heard about the new with-slots.  I think we should add
with-accessors to the spec.
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