Found via `codespell`

Removed redundant precompiled header include

Speedup MedianFilter::apply(), avoid to newly create the two GpuMat every time calling filter->apply(), which is very time consuming.

* remove overloads with explicit buffer, now BufferPool is used
* added async versions for all reduce functions

Conflicts:
	modules/core/include/opencv2/core/cuda.hpp
	modules/cudacodec/src/thread.cpp
	modules/cudacodec/src/thread.hpp
	modules/superres/perf/perf_superres.cpp
	modules/superres/src/btv_l1_cuda.cpp
	modules/superres/src/optical_flow.cpp
	modules/videostab/src/global_motion.cpp
	modules/videostab/src/inpainting.cpp
	samples/cpp/stitching_detailed.cpp
	samples/cpp/videostab.cpp
	samples/gpu/stereo_multi.cpp