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

diff --cc modules/calib3d/include/opencv2/calib3d.hpp
Simple merge

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

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

diff --cc modules/core/test/test_mat.cpp
Simple merge

diff --cc modules/dnn/src/dnn.cpp
Simple merge

diff --cc modules/dnn/test/test_misc.cpp
Simple merge

diff --cc modules/java/generator/gen_java.py
Simple merge

diff --cc modules/videoio/src/cap_dc1394_v2.cpp
Simple merge