Added scene.debugShowCommands

From the doc
> When true, commands are randomly shaded.  This is useful for performance analysis to see what parts of a scene or model are command-dense and could benefit from batching.

![image](https://f.cloud.github.com/assets/782098/1743551/bbac0dba-640e-11e3-870d-71bb49b3718e.png)

![image](https://f.cloud.github.com/assets/782098/1743560/cf92f6cc-640e-11e3-90dc-4366d99266ca.png)

No update to CHANGES.md