[openstreetmap-website] Content-Length on HEAD requests (#406)

[pnorman]

With a local test dataset and the server running with `bundle exec rails server`

```
pnorman at merry:~$ curl -I "http://localhost:3000/api/0.6/node/1001"
HTTP/1.1 200 OK
Last-Modified: Sun, 30 Sep 2012 17:00:00 GMT
Content-Type: text/xml; charset=utf-8
Cache-Control: max-age=0, private, must-revalidate
X-Ua-Compatible: IE=Edge
X-Request-Id: a7857cfa97b141c34dd12f3bfcf19545
X-Runtime: 0.014998
Server: WEBrick/1.3.1 (Ruby/1.9.3/2011-10-30)
Date: Thu, 01 Aug 2013 08:07:48 GMT
Content-Length: 0
Connection: Keep-Alive
```

For an api.osm.org request
```
pnorman at merry:~$ curl -I "http://api.openstreetmap.org/api/0.6/node/2403305061"
HTTP/1.1 200 OK
Date: Thu, 01 Aug 2013 08:09:17 GMT
Server: Apache/2.2.22 (Ubuntu)
X-Powered-By: Phusion Passenger (mod_rails/mod_rack) 3.0.21
Cache-Control: max-age=0, private, must-revalidate
X-UA-Compatible: IE=Edge,chrome=1
X-Request-Id: 3c63d124ab46523e7326a5ecd1cb444f
X-Runtime: 0.010416
Last-Modified: Thu, 01 Aug 2013 08:00:28 GMT
Status: 200
Vary: Accept-Encoding
Content-Type: text/xml; charset=utf-8
```

Looks like apache is discarding it, or it's being produced by WEBrick.

---
Reply to this email directly or view it on GitHub:
https://github.com/openstreetmap/openstreetmap-website/issues/406#issuecomment-21921404
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