invoke in Swing thread to make double sure;

--- a/src/Pure/System/swing_thread.scala	Sun Aug 28 20:56:49 2011 -0700
+++ b/src/Pure/System/swing_thread.scala	Mon Aug 29 16:28:51 2011 +0200
@@ -52,7 +52,7 @@
     val timer = new Timer(time.ms.toInt, listener)
     timer.setRepeats(false)
 
-    def invoke() { if (first) timer.start() else timer.restart() }
+    def invoke() { now { if (first) timer.start() else timer.restart() } }
     invoke _
   }