explicitly refer to superclass

--- a/src/Tools/jEdit/src/prover/Prover.scala	Sun Jan 11 13:16:35 2009 +0100
+++ b/src/Tools/jEdit/src/prover/Prover.scala	Sun Jan 11 13:46:26 2009 +0100
@@ -28,13 +28,13 @@
   val command_decls = new HashSet[String]{
     override def +=(elem : String) = {
       decl_info.event(elem, Markup.COMMAND)
-      this += elem
+      super.+=(elem)
     }
   }
   val keyword_decls = new HashSet[String]{
     override def +=(elem : String) = {
       decl_info.event(elem, Markup.KEYWORD)
-      this += elem
+      super.+=(elem)
     }
   }
   private var initialized = false