Modify guid regex and test for malformed guids [MJ-660]

I added a 404 template as well with a small note about typos, but I wasn't sure how much information we wanted to give away.
![2013-11-13-084359_509x230_scrot](https://f.cloud.github.com/assets/3379265/1531694/b2007af0-4c6a-11e3-8035-98bbe63dc408.png)

All tests pass.