alternative urls added for the corbt VPS

As we discussed after class, here are an alternative set of URLs. The files are just being served statically by nginx. I have 2TB of monthly bandwidth that is essentially unused, so I don't think anyone should have problems downloading from there.

Here's my graph for the large file being downloaded from my server, it's the closest thing to a test case I can come up with. :)

![download-time-large](https://f.cloud.github.com/assets/176426/2176233/38152558-95ce-11e3-8ec8-84712c4ad3f3.png)