Tests and another fix for issue #1467

The following still breaks after the fix for issue #1467:

```
module M1
  def initialize()
    super()
  end
end

class C1
 include M1
end

C1.new
```

I believe this PR fixes the problem, the target_class swap seems to be redundant based on the swap that happens inside the class.c#mrb_include_module function.