Detect rename

Fix for #30 Moved/renamed files appear as added + removed file in diff. Builds upon RP #27 as this is a requirement for the devhub master.

![screen shot 2014-11-01 at 04 12 34](https://cloud.githubusercontent.com/assets/3469492/4870604/15e7d2b4-6175-11e4-8c32-9be45aadf00f.png)