introduce return_sequence instruction to mom

test/vool/to_mom/test_return.rb

@@ -15,10 +15,16 @@ module Vool
     def test_slot_is_set
       assert @stats.first.left
     end
+    def test_two_instructions_are_returned
+      assert_equal 2 ,  @stats.length
+    end
+    def test_second_is_return
+      assert_equal Mom::ReturnSequence,  @stats.last.class
+    end
     def test_slot_starts_at_message
       assert_equal :message , @stats.first.left[0]
     end
-    def test_slot_gets_self
+    def test_slot_gets_return
       assert_equal :return_value , @stats.first.left[1]
     end
     def test_slot_assigns_something