add a way to bend the type for register_value

specifically for factories, where we know the type of next_object even it is not specified

test/risc/test_register_slot.rb

@@ -73,26 +73,4 @@ module Risc
       assert_equal :message , inst.array.symbol
     end
   end
-  class TestRegisterSlot4 < MiniTest::Test
-    include HasCompiler
-    def setup
-      Parfait.boot!(Parfait.default_test_options)
-      @compiler = Risc.test_compiler
-      @r0 = RegisterValue.new(:message , :Message).set_compiler(@compiler)
-      @r0[:next_message][:return_address] << @r0
-    end
-    def test_instructions
-      assert_equal SlotToReg ,  @compiler.risc_instructions.next(1).class
-      assert_equal RegToSlot ,  @compiler.risc_instructions.next(2).class
-      assert_equal NilClass ,  @compiler.risc_instructions.next(3).class
-    end
-    def test_slot_to
-      assert_slot_to_reg 1 , :message, 1, :"message.next_message"
-      assert risc(1).register.compiler
-    end
-    def test_reg_to
-      assert_reg_to_slot 2 , :message, :"message.next_message" , 4
-      assert risc(2).register.compiler
-    end
-  end
 end