add "opencv2/core/utility.hpp" header to precomp.hpp

Opps.

Conflicts:
	modules/core/src/gl_core_3_1.cpp
	modules/core/src/opencl/convert.cl
	modules/cudaimgproc/src/cuda/canny.cu
	modules/cudastereo/perf/perf_stereo.cpp
	modules/gpu/perf/perf_imgproc.cpp
	modules/gpu/test/test_denoising.cpp
	modules/ocl/src/opencl/imgproc_resize.cl
	samples/cpp/Qt_sample/main.cpp

Simplify the code as @SpecLad suggested.