In make-resume-url: use argument session-id

(not instance-session-id) to create resume-url.

scheme/httpd/surflets/surflet-handler.scm

@@ -552,7 +552,7 @@
 ;; All arguments are numbers except PATH-STRING, which is a string.
 (define (make-resume-url path-string session-id continuation-counter continuation-id)
   (string-append path-string
-		 ";k" (number->string (instance-session-id)) 
+		 ";k" (number->string session-id)
 		 ";c" (number->string continuation-counter)
 		 "-" (number->string continuation-id)))