Spike client side fetch js source

An initial spike on an idea for displaying source code within error/failure output.

![screen shot 2014-08-13 at 22 01 46](https://cloud.githubusercontent.com/assets/104158/3905647/65218b64-22ea-11e4-8bd9-6d4bc9ba9867.png)

![screen shot 2014-08-14 at 08 18 18](https://cloud.githubusercontent.com/assets/104158/3914025/2f5ee4c6-2340-11e4-8bdb-eda896272e45.png)

This will be removed. Probably doesn't belong as part of this pull request either as it's specific to having clickable entries to open up specifically in vim.

For _that_ pull request, we'd need to tackle mapping URLs to their file system entries (server side) and providing configurable options for what the links should do e.g. like better_errors with mvim/textmate/sublime etc.