small rename and new test for layout

lib/register/register_reference.rb

@@ -98,7 +98,7 @@ module Register
     real_name = clazz_name.to_s.split('_').last.capitalize.to_sym
     clazz = Parfait::Space.object_space.get_class_by_name(real_name)
     raise "Class name not given #{real_name}" unless clazz
-    index = clazz.object_layout.index_of( instance_name )
+    index = clazz.object_layout.variable_index( instance_name )
     raise "Instance name=#{instance_name} not found on #{real_name}" unless index.is_a?(Numeric)
     return index #  the type word is at index 0, but layout is a list and starts at 1 == layout
   end