bug: suspendable put-bytevector.

bug: suspendable put-bytevector.

To reproduce, do something like

   ./pre-inst-env demos/websocket/8s-server.scm&
   chromium demos/websocket/ws-client.html
or
   icecat demos/websocket/ws-client.html

and reload browser window several times.  The server should produce a
backtrace like

18:59:44 janneke@dundal:~/src/8sync/bug [env]
$ ./pre-inst-env demos/websocket/8s-server.scm
;;; note: source file /home/janneke/src/8sync/bug/demos/websocket/8s-server.scm
;;;       newer than compiled /home/janneke/.cache/guile/ccache/2.2-LE-8-3.A/home/janneke/src/8sync/bug/demos/websocket/8s-server.scm.go
;;; note: auto-compilation is enabled, set GUILE_AUTO_COMPILE=0
;;;       or pass the --no-auto-compile argument to disable.
;;; compiling /home/janneke/src/8sync/bug/demos/websocket/8s-server.scm
;;; compiled /home/janneke/.cache/guile/ccache/2.2-LE-8-3.A/home/janneke/src/8sync/bug/demos/websocket/8s-server.scm.go
listening: 1236
Zzzzzzzz....
on-ws-connection: args=(#<<websocket-server> 249ed80> 1)
on-ws-message: args= (("/home/janneke/src/8sync/bug/demos/websocket/8s-server.scm"))
on-message: ws: "Hello, Web Socket!"
on-ws-message: args= (("/home/janneke/src/8sync/bug/demos/websocket/8s-server.scm"))
on-message: ws: "Say: AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA..."
While reading request:
In procedure fport_read: Connection reset by peer

*** Caught exception with key 'system-error and arguments: ("fport_write" "~A" ("Broken pipe") (32)) ***
In ice-9/boot-9.scm:
    829:9 19 (catch #t #<procedure 2530ba0 at 8sync/agenda.scm:638:11 ()> #<procedure 7f6432c26c30 at 8sync/a…> …)
    829:9 18 (catch #t #<procedure 2530da0 at 8sync/agenda.scm:638:11 ()> #<procedure 7f6432c26c30 at 8sync/a…> …)
    829:9 17 (catch #t #<procedure 2530fa0 at 8sync/agenda.scm:638:11 ()> #<procedure 7f6432c26c30 at 8sync/a…> …)
    829:9 16 (catch #t #<procedure 2517d60 at 8sync/agenda.scm:638:11 ()> #<procedure 7f6432c26c30 at 8sync/a…> …)
    829:9 15 (catch #t #<procedure 2503640 at 8sync/agenda.scm:638:11 ()> #<procedure 7f6432c26c30 at 8sync/a…> …)
In 8sync/actors.scm:
    596:6 14 (call-catching-coroutine #<procedure 2503600 at 8sync/actors.scm:611:7 ()> _)
    576:6 13 (call-catching-errors)
In ice-9/boot-9.scm:
    829:9 12 (catch #t #<procedure 2503600 at 8sync/actors.scm:611:7 ()> #<procedure 7f6432b8f958 at 8sync/ac…> …)
In 8sync/actors.scm:
   616:18 11 (_)
In ice-9/boot-9.scm:
    841:4 10 (with-throw-handler _ _ _)
In 8sync/systems/web.scm:
   167:10  9 (_ _ . _)
In web/response.scm:
    221:2  8 (write-response #<<response> version: (1 . 0) code: 400 reason-phrase: #f headers: ((content-len…> …)
In web/http.scm:
   1199:2  7 (write-response-line (1 . 0) 400 "Bad Request" #<closed: file 2702930>)
   1081:2  6 (write-http-version (1 . 0) #<closed: file 2702930>)
In ice-9/suspendable-ports.scm:
   662:12  5 (put-string #<closed: file 2702930> "HTTP/" _ _)
     83:4  4 (write-bytes #<closed: file 2702930> #vu8(72 84 84 80 47 54 76 101 106 51 78 104 110 122 74 116 …) …)
In unknown file:
           3 (port-write #<closed: file 2702930> #vu8(72 84 84 80 47 54 76 101 106 51 78 104 110 122 74 116 …) …)
In ice-9/boot-9.scm:
   752:25  2 (dispatch-exception _ _ _)
   751:25  1 (dispatch-exception 1 system-error ("fport_write" "~A" ("Broken pipe") (32)))
In 8sync/agenda.scm:
   597:23  0 (print-error-and-continue _ . _)

*** Caught exception with key 'wrong-type-arg and arguments: ("port-write" "Wrong type argument in position ~A (expecting ~A): ~S" (1 "open output port" #<closed: file 2702930>) (#<closed: file 2702930>)) ***
In ice-9/eval.scm:
    619:8 19 (_ #(#(#<directory (guile-user) 23ef140>)))
In ice-9/boot-9.scm:
   2312:4 18 (save-module-excursion _)
  3822:12 17 (_)
In 8sync/actors.scm:
    812:6 16 (run-hive #<<hive> 28a6500> _ #:cleanup _ #:handle-signals _)
In ice-9/control.scm:
    91:24 15 (call-with-escape-continuation _)
In 8sync/agenda.scm:
    568:6 14 (run-agenda #<<agenda> queue: (() . #f) prompt-tag: ("prompt") read-port-map: #<hash-table 24f18…> …)
    631:5 13 (agenda-run-once! #<<agenda> queue: (() . #f) prompt-tag: ("prompt") read-port-map: #<hash-table …>)
In ice-9/boot-9.scm:
    829:9 12 (catch #t #<procedure 2c67d40 at 8sync/agenda.scm:638:11 ()> #<procedure 7f6432c26c30 at 8sync/a…> …)
    829:9 11 (catch #t #<procedure 2ebbf20 at 8sync/agenda.scm:638:11 ()> #<procedure 7f6432c26c30 at 8sync/a…> …)
    829:9 10 (catch #t #<procedure 2530120 at 8sync/agenda.scm:638:11 ()> #<procedure 7f6432c26c30 at 8sync/a…> …)
    829:9  9 (catch #t #<procedure 25304e0 at 8sync/agenda.scm:638:11 ()> #<procedure 7f6432c26c30 at 8sync/a…> …)
In 8sync/actors.scm:
    596:6  8 (call-catching-coroutine #<procedure 25304a0 at 8sync/actors.scm:611:7 ()> _)
    576:6  7 (call-catching-errors)
In ice-9/boot-9.scm:
    829:9  6 (catch #t #<procedure 25304a0 at 8sync/actors.scm:611:7 ()> #<procedure 7f6432b8f958 at 8sync/ac…> …)
In 8sync/actors.scm:
   616:18  5 (_)
In 8sync/systems/websocket/server.scm:
   171:11  4 (websocket-server-send _ #<<message> id: "f89a760cec1b14c9c6654de548156342:8" to: #("<websocket-…> …)
In ice-9/suspendable-ports.scm:
     83:5  3 (write-bytes #<closed: file 2702930> #vu8(83 97 121 58 32 65 65 65 65 65 65 65 65 65 65 65 65 # …) …)
In unknown file:
           2 (port-write #<closed: file 2702930>)
In ice-9/boot-9.scm:
   751:25  1 (dispatch-exception 0 wrong-type-arg ("port-write" "Wrong type argument in position ~A (expect…" …))
In 8sync/agenda.scm:
   597:23  0 (print-error-and-continue _ . _)

Zzzzzzzz....
  C-c C-c

The problem does not occur when enabling these lines

  (define put-bytevector (@ (ice-9 binary-ports) put-bytevector))
  (module-define! (resolve-module '(8sync systems websocket frame)) 'put-bytevector put-bytevector)

in demos/websocket/8s-server.scm

* demos/websocket/ws-client.html: New file.
* demos/websocket/8s-server.scm: New file.