Merge commit '43aec5ad' into merge-2.4

Conflicts:
	cmake/OpenCVConfig.cmake
	cmake/OpenCVLegacyOptions.cmake
	modules/contrib/src/retina.cpp
	modules/gpu/doc/camera_calibration_and_3d_reconstruction.rst
	modules/gpu/doc/video.rst
	modules/gpu/src/speckle_filtering.cpp
	modules/python/src2/cv2.cv.hpp
	modules/python/test/test2.py
	samples/python/watershed.py

apps/traincascade/CMakeLists.txt

@@ -34,4 +34,3 @@ if(ENABLE_SOLUTION_FOLDERS)
 endif()
 
 install(TARGETS ${the_target} RUNTIME DESTINATION bin COMPONENT main)
-