Explicitly linking to a Python framework on OS X prevents modules from
being built against one python (i.e. system python) and imported from
another (i.e. Homebrew python); the interpreter segfaults if there's a
linkage to a foreign python. Building the module with `-undefined
dynamic_lookup` instead of an explicit link allows the symbols to be
resolved at load time from a compatible python.

A difference of two pointers was casted to unsigned which can lead to
overflow on 64-bit systems.

Add all dirs from CUDA_LIBS_PATH as -L linker options to
OPENCV_LINKER_LIBS. These will end up in opencv.pc.

previous implementation was not thread/stream safe, since it used constant
memory

new implementation doesn't use any global objects, so it is thread/stream safe

Add GPU models in seperate folder, only old models are supported and they were replaced to make the CPU interface work.
This solves the undesired consequence of breaking the GPU interface.

move hog::set_up_constants from constructor to compute method

if user changed CUDA device between constructor and computation,
some variables were uninitialized