Fix display hosts in oneboxer

As mentioned in ["BBC Oneboxing Weirdness"](http://meta.discourse.org/t/bbc-oneboxing-weirdness/3994/2), the onebox displays only the last two elements of a domain, presumably to hide the www-part. But it also strips down `news.bbc.co.uk` to `co.uk`, which is obviously wrong. This commit fixes that.

![Screen Shot 2013-03-02 at 00 56 02](https://f.cloud.github.com/assets/233676/212006/9cde7c9e-82cb-11e2-889c-c48fa268e8eb.png)