Merged a few more changes from the trunk.

svn: r17964

collects/2htdp/private/universe.ss

@@ -210,7 +210,7 @@
  iworld3)
 
 ;; --- the server representation of a world --- 
-(define-struct iworld (in out name info) #:transparent)
+(define-struct iworld (in out name info) #; #:transparent)
 ;; World = (make-iworld IPort OPort Symbol [Listof Sexp])
 
 (define (iw* n) (make-iworld (current-input-port) (current-output-port) n '()))

collects/handin-server/run-servlet.ss

@@ -69,7 +69,8 @@
   (define ach (make-async-channel))
   ;; wrap the dispatcher so we can post on the waiting semaphore
   (define (wrap-sequence . ds)
-    (let ([d (apply sequencer:make ds)])
+    (let* ([ds (filter values ds)] ;; drop #f when log-file is #f
+           [d (apply sequencer:make ds)])
       (lambda (conn req)
         (d conn req)
         ;; (cond [(hash-ref port->sema (connection-o-port conn) #f)