Add this note about use of permutation_iterator in CUDA set_intersection.
Add this note about use of permutation_iterator in CUDA set_intersection.

--HG--
extra : convert_revision : svn%3A83215879-3e5a-4751-8c9d-778f44bb06a5/trunk%40821

jbrownbridge/thrust,jbrownbridge/thrust,jbrownbridge/thrust,jbrownbridge/thrust