Explain why older changes are hidden more clearly
Fixes T9920. When hiding changes, tell users why so they can learn the comment rule (usually, "Changes from before your most recent comment are hidden."; sometimes they're hidden for pagination reasons).
Also use "Show Older Comments" instead of "Show older comments." for the action since I think it's a little more consistent to use title case for links/actions?
- Viewed a task with a lot of comments, saw a "most recent comment" element.
- Artificially set page size to 3, saw a "lots of changes" hide.
- Grepped for removed string.
- Clicked both "show older stuff" links.
Reviewed By: chad
Maniphest Tasks: T9920
Differential Revision: https://secure.phabricator.com/D14719