Add findOrigin() method for find class origin

class.go

@@ -6,8 +6,10 @@ import (
 )
 
 var (
-	FlagClassIsInherited  = uint32(1 << 17)
 	FlagUndefinedAllocate = uint32(1 << 6)
+	FlagClassIsInherited  = uint32(1 << 17)
+	FlagClassIsOrigin     = uint32(1 << 18)
+	FlagClassIsPrepended  = uint32(1 << 19)
 )
 
 type methodTable map[Symbol]Method
@@ -252,6 +254,26 @@ func (mrb *State) checkInheritable(super RClass) {
 	}
 }
 
+func findOrigin(class RClass) RClass {
+	isNilClass := reflect.ValueOf(class).IsNil()
+	if isNilClass {
+		return nil
+	}
+
+	ret := class
+	if (ret.Flags() & FlagClassIsPrepended) != 0 {
+		ret = ret.Super()
+
+		for {
+			if (ret.Flags() & FlagClassIsOrigin) == 0 {
+				ret = ret.Super()
+			}
+		}
+	}
+
+	return ret
+}
+
 func allocObject(mrb *State, self Value) Value {
 	args := mrb.GetArgv()
 	argc := mrb.GetArgc()

object.go

@@ -50,7 +50,13 @@ func (obj *Object) ivGet(sym Symbol) Value {
 	return obj.iv.Get(sym)
 }
 
+func (mrb *State) includeModuleAt(class, insPos, module RClass, superSearch int) int {
+	return 0
+}
+
 func (mrb *State) IncludeModule(class, module RClass) error {
+	mrb.includeModuleAt(class, findOrigin(class), module, 1)
+
 	return nil
 }