simple_dialog: allow scala.swing.Component as well;

--- a/src/Pure/library.scala	Sat Aug 07 22:43:57 2010 +0200
+++ b/src/Pure/library.scala	Sat Aug 07 23:02:19 2010 +0200
@@ -89,8 +89,9 @@
     (parent: Component, title: String, message: Any*)
   {
     Swing_Thread.now {
+      val java_message = message map { case x: scala.swing.Component => x.peer case x => x }
       JOptionPane.showMessageDialog(parent,
-        message.toArray.asInstanceOf[Array[AnyRef]],
+        java_message.toArray.asInstanceOf[Array[AnyRef]],
         if (title == null) default_title else title, kind)
     }
   }