url.to_file_path() fails for unix:///C:/windows/path

Windows now supports Unix domain sockets.

If I parse a unix:// URL with a Windows path, then try to get the path back, I get an error:

extern crate url;
use url::Url;

fn main() {
    let path = "C:\\path\\to\\file";
    let file_url = "file:///C:/path/to/file";
    let unix_url = "unix:///C:/path/to/file";

    let mut one = Url::from_file_path(path).unwrap();
    let _ = one.set_scheme("unix").unwrap();
    assert_eq!(one.to_file_path().unwrap().as_os_str(), path);

    let two = Url::parse(file_url).unwrap();
    assert_eq!(two.to_file_path().unwrap().as_os_str(), path);

    let three = Url::parse(unix_url).unwrap();
    assert_eq!(three.to_file_path().unwrap().as_os_str(), path); // <-- panic!
}

PS C:\projects\rs-url-roundtrip> target\debug\rs-url-roundtrip.exe
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: ()', libcore\result.rs:945:5

As the code shows, the from_file_path/to_file_path round trip works, as does the parse/to_file_path round trip for a file:// URL. It would be great if the parse/to_file_path worked for unix:// as well.

Start by locating the implementation of Url::to_file_path and the existing file-URL path conversion tests. Reproduce the Windows unix:///C:/path/to/file case from the issue, then add coverage showing the expected path conversion and run the relevant test suite to confirm the regression is fixed.