I’m not entirely sure how versioning works with Blender, but it does say 2.78.5 in my version. If I remember correctly, I downloaded it a few weeks ago from the experimental download section. It seems they have moved towards 2.79 release candidate now, so I’d try downloading that. Also, the option is fairly hidden – but if it is present in your version, it will be on the ‘Render Layers’ tab (second from the left) in Properties panel, at the very bottom.
