bug in auto-integrator

The auto-integrator is not correctly hygienic.  In the following
configuration, the procedure BAZ from the BAZ structure should yield
the list (FOO BAR), not the list (FOO FOO) or the list (BAR BAR).

(define-structure foo (export foo)
  (open scheme)
  (optimize auto-integrate)
  (begin
    (define *foo* 'FOO)
    (define (foo) *foo*)))

(define-structure bar (export bar)
  (open scheme)
  (optimize auto-integrate)
  (begin
    (define *foo* 'BAR)
    (define (bar) *foo*)))

(define-structure baz (export baz)
  (open scheme foo bar)
  (optimize auto-integrate)
  (begin
    (define (baz)
      (list (foo) (bar)))))