Default to latest file when picking from multiple available patches

This makes it so that hitting "enter" when choosing between multiple patches will select the latest patch, not the oldest. Verify with a ticket with multiple patches, e.g. 29546:

![image](https://cloud.githubusercontent.com/assets/442115/4784655/995cf854-5d60-11e4-9572-c9b4ca06f87d.png)

(per suggestion by @markjaquith)