Spurious initial slash in empty relative path when calling .path() accessor

```javascript
URI("/a/b/c/").
    relativeTo("/a/b/c/").
    toString() === "";
// Good!

URI("/a/b.c/").
    relativeTo("/a/b/c/").
    path() === "/";
// Bad!

URI("").toString() === ""; // Good!

URI("").path() === "/"; // Bad!
```

* 8d0c31c adds test cases demonstrating this problem.
* 8049654 fixes the problem.

Please see the commit logs for rationale behind the changes made.