create a reduce_int on RegisterSlot

that just passes through to RegisterValue by calling to_reg

lib/slot_machine/macro/get_internal_word.rb

@@ -2,7 +2,7 @@ module SlotMachine
   class GetInternalWord < Macro
     def to_risc(compiler)
       compiler.builder(compiler.source).build do
-        integer = message[:arg1].to_reg.reduce_int(false)
+        integer = message[:arg1].reduce_int(false)
         message[:return_value] << message[:receiver][integer]
       end
     end