FromStr impl for extra::url::Url drops the last digit of port

This program

```
extern mod extra;

use extra::url::Url;

fn main() {
    printfln!(FromStr::from_str::<Url>("scheme://host:1234"));
}
```

outputs

```
Some({scheme: ~"scheme", user: None, host: ~"host", port: Some(~"123"), path: ~"", query: ~[], fragment: None})
```
