use the return jump to jump to the return sequence

thus every method only has one exit
should make multi return messages smaller
especially when we have escape analisis
(maybe will help with inlining too)

lib/vool/return_statement.rb

@@ -18,7 +18,7 @@ module Vool
     def to_mom( compiler )
       ret = Mom::SlotLoad.new( [:message , :return_value] ,
                         @return_value.slot_definition(compiler) )
-      ret << Mom::ReturnSequence.new
+      ret << Mom::ReturnJump.new
     end
 
     def to_s(depth = 0)