I propose forEach method for cv::Mat and cv::Mat_.
This is solution for the overhead of MatIterator_<_Tp>.

I runs a test that micro opecode runs all over the pixel of cv::Mat_<cv::Point3_<uint8_t>>.
And this implementation 40% faster than the simple pointer, 80% faster than iterator.
With OpenMP, 70% faster than simple pointer, 95% faster than iterator (Core i7 920).

Above all, code is more readable.

My test code is here.
    https://gist.github.com/kazuki-ma/8285876

Thanks.

Conflicts:
	modules/core/include/opencv2/core/internal.hpp
	modules/core/src/arithm.cpp
	modules/imgproc/src/imgwarp.cpp
	modules/objdetect/src/hog.cpp

 - all parsed headers are included into "cv2.cpp" with "pyopencv_generated_include.h"
 - types starting with "Ptr_" converted to "Ptr<...>" form (avoids many typedefs in "cv2.cpp")

call dst.create(...) before using it