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
```
That would belong in a more integration-oriented test rather than these unit tests. I tried to make heads or tails of the resource functional tests but wasn't sure how to add new stuff there.