Release 4.9

This is a tracking issue for release 4.9.

**Please keep feature requests in their own issues**

If you want to make a comment on a particular change, please make the comment in the "Files changed" tab so comments are not lost during a rebase (they may occur on patches to the previous release).

List of changes for release:
- [x] Add `res.sendStatus` #2297
- [x] Fix behavior of `req.subdomains` for IP hostnames #2308
- [x] Provide client aborted error from `res.sendFile` #2305
- [x] Support `X-Forwarded-Host` in `req.subdomains`

**Testing this release**

If you want to try out this release, you can install it with the following command:
```bash
$ npm install visionmedia/express#4.9
```

Owners/collaborators: please do not merge this PR :)