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

diff --cc CMakeLists.txt
Simple merge

diff --cc cmake/OpenCVCompilerOptions.cmake
Simple merge

diff --cc cmake/OpenCVUtils.cmake
Simple merge

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

diff --cc modules/core/CMakeLists.txt
Simple merge

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

diff --cc samples/python/contours.py
Simple merge

diff --cc samples/python/digits_video.py
Simple merge