removing those ugly slot index constants

The constants were bad enough,
but they were also at the wrong level

Now register level is defining mappings from
symbol names to indexes, by using the layout

lib/virtual/slots/frame_slot.rb

@@ -2,9 +2,9 @@ module Virtual
 
   # Slots in the Frame a re represented by instances of FrameSlot
 
-  # Slots in the Frame are local or temporary varialbes in a message
+  # Slots in the Frame are local or temporary variables in a message
   class FrameSlot < Slot
-    def initialize index , type = Unknown, value = nil
+    def initialize type = Unknown, value = nil
       super
     end
   end