invoke later to reduce chance of causing deadlock;

--- a/src/Pure/System/swing_thread.scala	Tue Feb 21 16:28:18 2012 +0100
+++ b/src/Pure/System/swing_thread.scala	Tue Feb 21 16:42:57 2012 +0100
@@ -53,7 +53,7 @@
     val timer = new Timer(time.ms.toInt, listener)
     timer.setRepeats(false)
 
-    def invoke() { now { if (first) timer.start() else timer.restart() } }
+    def invoke() { later { if (first) timer.start() else timer.restart() } }
     invoke _
   }