Fixed running tests on Windows

I've had problems running tests on Windows that I've narrowed down to a simple test that includes a relative resource. For the `relative.html` test in this patch before applying my fixes in `options.js` I got the following results:

![paths-oh-my](https://f.cloud.github.com/assets/742941/914838/816e26fe-fe4e-11e2-97c3-12f51c1e80f5.png)

This patch fixes these problems (with tests) and also fixes the path resolution of tests to work correctly when using the `--prefix` and `--server` options (previously the tests for these were failing in the `1-args.js` test when run on Windows).

These changes supersede #2, which didn't correctly handle absolute paths.