Put requested post in middle of page

This came out of my post here: http://bbs.boingboing.net/t/can-i-search-the-posts-in-a-topic/22929/4?u=riking

I noticed that clicking the same-thread search results was a bit wacky in terms of where the post would end up, so I said that the post should be about 33% down the page. After trying that out, it seems that 20% is a more sensible amount, so that's what I'm PRing right now.

Here is a full-size screenshot of my development instance with this new behavior in the `jumpToPost` method: http://i.imgur.com/ZsqvuvU.png

The requested post (`/5`) was the one by `pekka​.​gaiser`.

Additionally, I ~~changed~~ hacked the keyboard shortcuts to use `jumpToPost` when inside a topic.