fixed the CTM renderer to properly average values if the colored light core is installed

I bit crammed values into the light integers you guys were using in your CTM renderer.  This broke your averaging routine that added them together and divided by four or two, as that algorithm allowed channels to flow into the one below when the sum was divided by two or four.  I wrote a method that can average any number of packed-light-values along each 4 bit channel, and implemented it in your CTM renderer.

There IS a slightly larger performance drop here, but it shouldn't be noticeable.  To put it in perspective, rendering an anvil is WAY worse in complexity. Also, this method only runs once per block, then it's done until the object is removed from the render buffer (till the player walks away) so the added complexity should be far from noticeable.

If you are still concerned, feel free to discuss your concerns here, or on IRC.

Old:
![giv73if](https://cloud.githubusercontent.com/assets/5491723/5500781/36f91b96-871a-11e4-9c37-77b43e966c2f.jpg)

New:
![rtmxleo](https://cloud.githubusercontent.com/assets/5491723/5500779/2e2fab24-871a-11e4-912c-d3a50c68df8e.jpg)