In 405156b1 I added a small feature so that /newest has a line marking where the logged-in user last loaded /newest.

Response has been positive (and it's easy to adblock for the folks who don't like it), so I'd like to copy over the functionality to the equivalent page for comments, /comments.

There's also a small bug to fix in last_read_newest; HomeController#newest calls touch even if the 'last read line' isn't shown. So the user Alice reads /newest and leaves for a few days and 30 stories are submitted, so the line should appear 5 spots down on page 2. Alice loads /newest and the line isn't visible because all stories are new. She clicks to page 2 and the line does not appear because loading page 1 already touched the timestamp. Maybe this calls for a helper to share the @user&.last_read_newest&.after?(story.created_at) logic from app/views/home/index.html.erb, I think if it returned the new value for already_printed_newest_line, the controller would know to touch the value and view would know to not print it twice.