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

diff --cc cmake/OpenCVDetectInferenceEngine.cmake
Simple merge

diff --cc modules/core/include/opencv2/core/cvdef.h
Simple merge

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

diff --cc modules/dnn/misc/python/test/test_dnn.py
Simple merge

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

diff --cc modules/dnn/src/op_inf_engine.hpp
Simple merge

diff --cc modules/dnn/test/test_common.hpp
Simple merge

diff --cc modules/dnn/test/test_common.impl.hpp
Simple merge

diff --cc modules/imgproc/misc/java/test/ImgprocTest.java
Simple merge

diff --cc modules/imgproc/test/test_convhull.cpp
Simple merge

diff --cc modules/objdetect/src/qrcode.cpp
Simple merge