shared-array composition bug

[Kevin Ryde]

The cvs seems to have a bug in making a shared array from what's
already a shared array,

        (define a #2((1 2 3) (4 5 6) (7 8 9)))

        (define s (make-shared-array a (lambda (i) (list i 1)) 3))
        (display s) (newline)

        (define t (make-shared-array s list '(1 2)))
        (display t) (newline)

"s" is a shared array which is column 1 of "a", ie. (2 5 8).  "t" is
meant to be range 1 to 2 of "s", ie. (5 8), but it comes out as (4 7).

        #(2 5 8)
        address@hidden(4 7)

This works in 1.6, so I'm guessing it's some recent regression.