Improve rendering of previews in Facebook links

(Bug, Investigate , Priority: High, Test Status: No automated tests yet , Reported By Justin du Coeur, )
Social Networking
Summary: For example, look at how this renders.
We should be smarter about internal links.
We should probably have an alternate View specifically for this -- a Preview View, or something like that -- and an alternate Wikitext renderer for it. The Preview View (Sharing View?) would be a Very Good Thing, but it doesn't save us from needing better defaults if it's not specified.