Python typdef fixed. Reverted the example to MOG2. Not time to make the command line switch for now.

get_hogdescriptor_visu is passed img->clone(), which is not usable
as a non-const reference (and it doesn't modify the argument, anyway).

Conflicts:
	cmake/OpenCVDetectPython.cmake
	cmake/OpenCVModule.cmake
	modules/core/src/gpumat.cpp
	modules/cudaimgproc/test/test_hough.cpp
	modules/gpu/CMakeLists.txt
	modules/gpu/src/cuda/generalized_hough.cu
	modules/gpu/src/generalized_hough.cpp
	modules/python/CMakeLists.txt