Add a macro for defining has_nested_type traits
Add a macro for defining has_nested_type traits

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