remove ad_transfer in save_message

towards removing all add_
change to set_builder and chaining in reg values

test/risc/test_builder.rb

@@ -45,15 +45,13 @@ module Risc
       assert_equal Transfer , built.next.class
     end
     def test_returns_slot
-      r2 = RegisterValue.new(:r2 , :Message)
-      r2.builder = @builder
+      r2 = RegisterValue.new(:r2 , :Message).set_builder( @builder )
       built = @builder.build{ r2 << space![:next_message] }
       assert_equal SlotToReg , built.class
       assert_equal :r1 , built.array.symbol
     end
     def test_returns_slot_reverse
-      r2 = RegisterValue.new(:r2 , :Message)
-      r2.builder = @builder
+      r2 = RegisterValue.new(:r2 , :Message).set_builder( @builder )
       built = @builder.build{ r2 << space![:next_message] }
       assert_equal SlotToReg , built.class
       assert_equal :r1 , built.array.symbol