keep diagnostic command -- avoid confusion when it disappears;

--- a/src/Tools/jEdit/src/active.scala	Mon Dec 10 19:17:16 2012 +0100
+++ b/src/Tools/jEdit/src/active.scala	Mon Dec 10 19:28:56 2012 +0100
@@ -55,7 +55,6 @@
                 }
 
               case XML.Elem(Markup(Markup.GRAPHVIEW, Position.Id(exec_id)), body) =>
-                try_replace_command(exec_id, "")
                 default_thread_pool.submit(() =>
                   {
                     val graph =