[SoC] gdalwarp now with 100% more OpenCL code!

[Seth Price]

For my Summer of Code project I've been rewriting GDAL's warping core  
to run on the GPU via OpenCL. It's not fully tested yet, but I here's  
what I have:

http://github.com/mailseth/OpenCL-integration-for-GRASS---GDAL

Feel free to play with it and tell me how it goes. If you find any  
problems, please email me a helpful bug report with sample imagery and  
the command you're using. It should work with the cubic, cubicspline,  
& lanzcos resampling methods. The makefile is currently set up for  
Mac, I'm not sure how to do it for linux/windows, and I don't have a  
machine to test that on. If you get something working, please send it  
my way.

I've been able to warp some basic, small, imagery with almost  
identical results to the regular warper. The only difference is around  
the raster's edges, where I believe the OpenCL code does a better job.
~Seth