RFC 17 implementation

This branch implements [Chef RFC 17](https://github.com/opscode/chef-rfc/blob/master/rfc017-file-specificity.md). I've only run the unit tests as many of the others seem to take a very long time and some break due to TTY issues:

```
Finished in 2 minutes 14.7 seconds
6864 examples, 0 failures, 30 pending
```
This seemed safer as it is the lowest point in the stack and thus less likely to break unrelated code.