Stitcher will now make a working copy of the CameraParams object to avoid side effects when composing Panorama.
Makes it possible to estimate transform once and then compose multiple panoramas. Useful for setup with fixed cameras.

Warping a matrix with more than 4 channels using BORDER_CONSTANT and
INTER_NEAREST, INTER_CUBIC or INTER_LANCZOS4 interpolation led to
undefined behaviour. This commit changes the behavior of these methods
to be similar to that of INTER_LINEAR. Changed the scope of some of the
variables to more local. Modified some tests to be able to detect the
error described.

#resolves: 7881

remove printf statement and associated variables from invMapPointSpherical() in undistort.cpp

* Improve documentation.

* Update imgproc.hpp

Implement cv::cuda::calcHist with mask support (#8367)

* Implement cuda::calcHist with mask

* Fix documentation build warning

* Have their own step sizes for src and mask. Fix review comment.

3.2 version doesn't support 4 channel color image
detections, unlike 3.1. Now, we don't call
CV_Error() if 4 channel image is given.

resolve #8326

Fix grammar error in py_features_meaning.markdown (#8378)

`template<typename _Tp> inline const _Tp* Mat_<_Tp>::operator [](int y) const` does not support 3d matrix since it checks rows.

This operator[] shall check size.p[0] instead.