Merge remote-tracking branch 'origin/2.4'

Merge remote-tracking branch 'origin/2.4'

Conflicts:
	3rdparty/ffmpeg/ffmpeg_version.cmake
	cmake/OpenCVFindLibsGrfmt.cmake
	cmake/templates/cvconfig.h.cmake
	modules/bioinspired/doc/retina/index.rst
	modules/calib3d/doc/camera_calibration_and_3d_reconstruction.rst
	modules/calib3d/src/precomp.hpp
	modules/contrib/src/inputoutput.cpp
	modules/contrib/src/precomp.hpp
	modules/core/include/opencv2/core/internal.hpp
	modules/core/include/opencv2/core/types_c.h
	modules/core/src/drawing.cpp
	modules/core/src/precomp.hpp
	modules/core/src/system.cpp
	modules/features2d/doc/common_interfaces_of_descriptor_matchers.rst
	modules/features2d/doc/common_interfaces_of_feature_detectors.rst
	modules/features2d/include/opencv2/features2d/features2d.hpp
	modules/features2d/src/precomp.hpp
	modules/flann/src/precomp.hpp
	modules/gpu/doc/camera_calibration_and_3d_reconstruction.rst
	modules/gpu/doc/image_filtering.rst
	modules/gpu/doc/image_processing.rst
	modules/gpu/doc/video.rst
	modules/gpu/perf/perf_imgproc.cpp
	modules/gpu/perf4au/main.cpp
	modules/gpu/src/imgproc.cpp
	modules/gpu/src/precomp.hpp
	modules/gpu/test/test_imgproc.cpp
	modules/highgui/CMakeLists.txt
	modules/highgui/test/test_precomp.hpp
	modules/imgproc/doc/structural_analysis_and_shape_descriptors.rst
	modules/imgproc/src/precomp.hpp
	modules/java/generator/src/cpp/Mat.cpp
	modules/legacy/src/precomp.hpp
	modules/ml/doc/k_nearest_neighbors.rst
	modules/ml/src/precomp.hpp
	modules/nonfree/doc/feature_detection.rst
	modules/nonfree/src/precomp.hpp
	modules/objdetect/include/opencv2/objdetect/objdetect.hpp
	modules/objdetect/src/cascadedetect.cpp
	modules/objdetect/src/hog.cpp
	modules/objdetect/src/precomp.hpp
	modules/objdetect/test/test_latentsvmdetector.cpp
	modules/ocl/src/hog.cpp
	modules/ocl/src/opencl/objdetect_hog.cl
	modules/ocl/src/precomp.hpp
	modules/photo/src/precomp.hpp
	modules/stitching/src/precomp.hpp
	modules/superres/perf/perf_precomp.hpp
	modules/superres/src/optical_flow.cpp
	modules/superres/src/precomp.hpp
	modules/superres/test/test_precomp.hpp
	modules/ts/include/opencv2/ts.hpp
	modules/video/src/precomp.hpp
	modules/videostab/src/precomp.hpp
	modules/world/src/precomp.hpp