fix refinements/prepend bug

replaced method entry should be invalidated.
[Bug #17386]

class.c

@@ -1110,6 +1110,8 @@ move_refined_method(ID key, VALUE value, void *data)
     struct rb_id_table *tbl = RCLASS_M_TBL(klass);
 
     if (me->def->type == VM_METHOD_TYPE_REFINED) {
+        rb_clear_method_cache(klass, me->called_id);
+
         if (me->def->body.refined.orig_me) {
 	    const rb_method_entry_t *orig_me = me->def->body.refined.orig_me, *new_me;
 	    RB_OBJ_WRITE(me, &me->def->body.refined.orig_me, NULL);

test/ruby/test_refinement.rb

@@ -2446,4 +2446,31 @@ class TestRefinement < Test::Unit::TestCase
   def eval_using(mod, s)
     eval("using #{mod}; #{s}", Sandbox::BINDING)
   end
+
+  # [Bug #17386]
+  def test_prepended_with_method_cache
+    foo = Class.new do
+      def foo
+        :Foo
+      end
+    end
+
+    code = Module.new do
+      def foo
+        :Code
+      end
+    end
+
+    _ext = Module.new do
+      refine foo do
+        def foo; end
+      end
+    end
+
+    obj = foo.new
+
+    assert_equal :Foo, obj.foo
+    foo.prepend code
+    assert_equal :Code, obj.foo
+  end
 end