Admin: Comment system changes

I've done a lot of hacking to the comment system (a much-hacked Pollxn) to make some minor improvements recently… I think it's all working right, but please tell me if it isn't.

The details, for those who care

You'll be glad to know that I've finally managed to add to the notification emails a link back to the thread and the actual title of the post. (As obvious as those seem, that data wasn't available to the program until after a new post was processed. It took some rearrangement of the code to get that data before processing.)

I've also replaced '0 comments' with 'leave a comment' on the blog page. As trivial as that was, I don't know why I didn't think of it ages ago.

I've got some minor tweaks left to do, including linking from the thread back to the blog post. fixing the "3 comments comment(s)" bug, and figuring out how to handle the "leave a comment" link on older posts where commenting is locked. But those'll come later.