revert to Thrust v1.2 fast_scan/safe_scan dispatch
revert to Thrust v1.2 fast_scan/safe_scan dispatch

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