Use vfs.FileSystem interface instead of vcs.FileSystem.

That should be all the references as far as I can find.

However, I see this repo vendors its dependencies. I've never used the `--copy=true` mode of `godep` before, and I tried to get it to work now, but I wasn't sure how to get it to pick up dependencies from all subpackages instead of just the Go package in the root folder... Any ideas?
No worries, I was just trying to determine if it was my change that caused the tests to fail, or something between that commit and commit before my change. It turned out it was my change after all. :)