Comment 1 for bug 175517

Fixed in revision 1223. Thanks.

> (define ctop
    (make-custom-textual-output-port
      "ctop"
      (lambda (str start count)
        (printf "*** (write! ~s)\n" (substring str start (+ start count)))
        count)
      #f #f #f))
> (textual-port? ctop)
#t
> (binary-port? ctop)
#f
> (write 'blah ctop)
*** (write! "blah")
> (newline ctop)
*** (write! "\n")