OpenCL DCT Denoise

I've just checked in an OpenCL implementation of the DCT de-noising algorithm I mentioned previously. I've only done the mono version so far.

It's not terribly fast - 10ms wall-clock for a 512x512 mono image, and given that it requires 64 DCT's per 8x8 block and needs to accumulate the results, it probably never will be.

The kernel source.Update: Colour version implemented now.