Merge remote-tracking branch 'origin/2.4' into merge-2.4

Conflicts:
	cmake/OpenCVDetectCUDA.cmake
	doc/tutorials/introduction/linux_gcc_cmake/linux_gcc_cmake.rst
	modules/core/CMakeLists.txt
	modules/features2d/perf/opencl/perf_brute_force_matcher.cpp
	modules/highgui/src/grfmt_tiff.cpp
	modules/imgproc/src/clahe.cpp
	modules/imgproc/src/moments.cpp
	modules/nonfree/CMakeLists.txt
	modules/ocl/perf/perf_ml.cpp
	modules/superres/CMakeLists.txt