added row_sum example
added row_sum example

--HG--
extra : convert_revision : svn%3A83215879-3e5a-4751-8c9d-778f44bb06a5/trunk%40728

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