Conflicts:
	CMakeLists.txt
	modules/highgui/src/cap.cpp
	modules/nonfree/src/surf.ocl.cpp
	modules/ocl/include/opencv2/ocl/ocl.hpp
	modules/ocl/src/color.cpp
	modules/ocl/src/gftt.cpp
	modules/ocl/src/imgproc.cpp
	samples/ocl/facedetect.cpp

Improve ocl cvt_color performance for the following conversions: RGB<->BGR, RGB->Gray, RGB<->XYZ, RGB<->YCrCb, RGB<->YUV, and mRGBA<->RGBA.
The improvement was done basically by processing more than 1 pixel by each work-item and using vector's operations.
new performance tests were added