Parameterize doesn't rewind correctly

[shirok]

When an error is thrown within guard procedure.

Reported by Joo ChurlSoo. Here's a sample session exhibiting the bug.

gosh> (use gauche.parameter)

gosh>
(define a (make-parameter 1 number->string))
(define b (make-parameter 2 number->string))
a
gosh> b
gosh> (list (a) (b))
("1" "2")
gosh> (parameterize ((a 10) (b 20) (a 30) (b 40)) (list (a) (b)))
("30" "40")
gosh> (list (a) (b))
("10" "20")
gosh> (a 1) (b 2)
"10"
gosh> "20"
gosh> (list (a) (b))
("1" "2")
gosh> (parameterize ((a 10) (b 20) (a 30) (b 'ab)) (list (a) (b)))
*** ERROR: number required: ab
Stack Trace:

---

0 (P L)
[unknown location]
1 (^ () (set! S (P L)) (set! S (P L)) (set! S (P L)) (set! S (P L)))
[unknown location]
2 (eval expr env)
At line 179 of "c:\tilde\gauche\share\gauche-0.9\0.9.4\lib/gauche/interactive.scm"
gosh> (list (a) (b))
("30" "20")
gosh> (let ((f (make-parameter 'a))
(path '())
(g (make-parameter 'g))
(c #f))
(let ((add (lambda () (set! path (cons (f) path)))))
(add)
(parameterize ((f 'b)
(g (call-with-current-continuation
(lambda (c0) (set! c c0) 'c))))
(add) (f (g)) (add))
(f 'd)
(add)
(if (< (length path) 5)
(c 'e)
(reverse path))))
(a b c d c e d) ;; cf. (a b c d b e d)

[shirok]

Fix pushed. 45e7262

The fix isn't ideal; we may revise it later.