Add failing test for (route/files "/")

Hey,

I've been using `(route/files "/")` as a fallback route for serving static files when doing development without nginx.

Curiously, after upgrading to Compojure 1.2.0 getting the root (i.e. http://localhost:3000)  will serve index.html with the content type application/octet-stream instead of text/html:

```
$ curl -I http://localhost:3000
HTTP/1.1 200 OK
Date: Sun, 19 Oct 2014 18:06:20 GMT
Last-Modified: Sun, 19 Oct 2014 00:17:04 GMT
Content-Length: 1981
Content-Type: application/octet-stream
Server: Jetty(7.6.8.v20121106)
```

Getting the index.html file explicitly will still use the correct content type:

```
$ curl -I http://localhost:3000/index.html
HTTP/1.1 200 OK
Date: Sun, 19 Oct 2014 18:07:54 GMT
Last-Modified: Sun, 19 Oct 2014 00:17:04 GMT
Content-Length: 1981
Content-Type: text/html
Server: Jetty(7.6.8.v20121106)
```

Here is a failing test demonstrating the issue. Downgrading to 1.1.9 makes the issue disappear.