Merge remote-tracking branch 'upstream/3.4' into merge-3.4

diff --cc cmake/OpenCVModule.cmake
Simple merge

diff --cc modules/core/include/opencv2/core/types.hpp
Simple merge

diff --cc modules/core/src/precomp.hpp
Simple merge

diff --cc modules/core/src/system.cpp
Simple merge

diff --cc modules/features2d/include/opencv2/features2d.hpp
Simple merge

diff --cc modules/imgproc/include/opencv2/imgproc.hpp
Simple merge

diff --cc modules/ml/src/rtrees.cpp
Simple merge