Test merge_by_key with thrust::device in __device__ code.
Test merge_by_key with thrust::device in __device__ code.

dachziegel/thrust,thvasilo/thrust,xiongzhanblake/thrust,xiongzhanblake/thrust_src,egaburov/thrust,sarvex/thrust,raygit/thrust,jaredhoberock/thrust,zhenglaizhang/thrust,marksantos/thrust,sdalton1/thrust,thrust/thrust,raygit/thrust,xiongzhanblake/thrust_src,Ricardo666666/thrust,andrewcorrigan/thrust-multi-permutation-iterator,dachziegel/thrust,egaburov/thrust,xiongzhanblake/thrust_src,Ricardo666666/thrust,sarvex/thrust,arnabgho/thrust,mohamed-ali/thrust,thrust/thrust,sarvex/thrust,thrust/thrust,GrimDerp/thrust,Ricardo666666/thrust,zeryx/thrust,zeryx/thrust,mohamed-ali/thrust,jaredhoberock/thrust,xiongzhanblake/thrust,thrust/thrust,jaredhoberock/thrust,thvasilo/thrust,thrust/thrust,xiongzhanblake/thrust,arnabgho/thrust,GrimDerp/thrust,thvasilo/thrust,sdalton1/thrust,andrewcorrigan/thrust-multi-permutation-iterator,GrimDerp/thrust,jaredhoberock/thrust,sdalton1/thrust,zeryx/thrust,egaburov/thrust,dachziegel/thrust,marksantos/thrust,zhenglaizhang/thrust,mohamed-ali/thrust,zhenglaizhang/thrust,arnabgho/thrust,raygit/thrust,jaredhoberock/thrust,marksantos/thrust,andrewcorrigan/thrust-multi-permutation-iterator