Enable on GPU the butterfly optimization of pyfaust.circ and anticirc.

src/faust_linear_operator/CPU/faust_TransformHelper.h

src/faust_linear_operator/CPU/faust_TransformHelper.hpp

...linear_operator/GPU2/faust_TransformHelperButterfly_gpu.h

...near_operator/GPU2/faust_TransformHelperButterfly_gpu.hpp

src/faust_linear_operator/GPU2/faust_TransformHelper_gpu.hpp

wrapper/python/pyfaust.py

wrapper/python/src/FaustCoreCppGPU.hpp