Highlight renames and copies in patchreviewer

`renames=copies` is part of the [recommended git configuration](https://drupal.org/node/1542048).

However, it's easy to not recognize that a file is renamed/copied, since the diff file headers are "greyed out".

This PR adds explicit highlighting for both cases:

![dreditor-highlight-renames](https://cloud.githubusercontent.com/assets/41992/3162619/138055be-eb37-11e3-9320-46656772b5e9.png)

_Sorry, screenshot additionally has #59 applied, but you get the point._