Provide optional notification of nested comment replies to the parent comment's author (beyond the initial reply).

Currently, if there is a reply to one of my comments, I receive a notice. However, if there is a reply to the reply, and so on, I don't. These grandchildren replies are often still relevant and of interest to me, however. Having the option of being notified of them would be nice.

(Alternately, this suggestion would solve the problem also, though that solution would require an additional step from the author.)