bug#24321: Guardian fails to protect procedure properties

[Robin Templeton]

The following expression produces possibly erroneous results in Guile
2.1.3.104-8f2f8 (with Debian's libgc1c2 version 1:7.4.2-8):

(let ((guardian (make-guardian))
      (foo (eval '(lambda () #f) (interaction-environment))))
  (set-procedure-property! foo 'wibbly 'wobbly)
  (guardian foo)
  (format #t "~S~%" (procedure-properties foo))
  (set! foo #f)
  (gc)
  (do ((foo (guardian) (guardian)))
      ((not foo))
    (format #t "~S~%" (procedure-properties foo))))

First it prints "((wibbly . wobbly))" as expected, but after the
procedure is retrieved from the guardian the list of properties is
empty. The properties are stored in a weak hash table, but shouldn't
they be protected from GC while the procedure is in the guardian?

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