Fix create object Asset Bundle with custom class in Bundle config


![2013-07-07 05 10 31](https://f.cloud.github.com/assets/683183/757427/099737ec-e6a2-11e2-9451-62352ef796bb.png)
![2013-07-07 05 07 49](https://f.cloud.github.com/assets/683183/757423/ae96301e-e6a1-11e2-9c9e-c995769061c4.png)