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

modules/core/test/test_io.cpp

@@ -406,7 +406,7 @@ protected:
             Vec<int, 5> v1(15, 16, 17, 18, 19), ov1;
             Scalar sc1(20.0, 21.1, 22.2, 23.3), osc1;
             Range g1(7, 8), og1;
-            
+
             FileStorage fs(fname, FileStorage::WRITE);
             fs << "mi" << mi;
             fs << "mv" << mv;