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

lishi0927/thrust,rdmenezes/thrust,UIKit0/thrust,rdmenezes/thrust,malenie/thrust,lishi0927/thrust,bfurtaw/thrust,rdmenezes/thrust,h1arshad/thrust,h1arshad/thrust,hemmingway/thrust,Vishwa07/thrust,google-code-export/thrust,malenie/thrust,lishi0927/thrust,levendlee/thrust,UIKit0/thrust,Vishwa07/thrust,levendlee/thrust,Vishwa07/thrust,hemmingway/thrust,allendaicool/thrust,julianromera/thrust,allendaicool/thrust,allendaicool/thrust,bfurtaw/thrust,julianromera/thrust,h1arshad/thrust,julianromera/thrust,UIKit0/thrust,levendlee/thrust,google-code-export/thrust,lishi0927/thrust,google-code-export/thrust,rdmenezes/thrust,julianromera/thrust,hemmingway/thrust,allendaicool/thrust,h1arshad/thrust,Vishwa07/thrust,UIKit0/thrust,bfurtaw/thrust,hemmingway/thrust,google-code-export/thrust,bfurtaw/thrust,malenie/thrust,levendlee/thrust,malenie/thrust