Merge branch 2.4

diff --cc apps/traincascade/boost.cpp
Simple merge

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

diff --cc modules/features2d/doc/feature_detection_and_description.rst
Simple merge

diff --cc modules/features2d/src/brisk.cpp
Simple merge

diff --cc modules/gpu/src/cascadeclassifier.cpp
Simple merge

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

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

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