Added workaround for Firefox not sending LINK in uppercase what then is ...

...denied by nginx.

More info: http://stackoverflow.com/questions/9645037/nginx-rejects-custom-http-methods-if-not-all-upper-case

The only problem I see by this is, that it will fail if the `framework.http_method_override` setting is set to `false` ... Any idea how I could check that? If that's set, I'd add a notice for all `LINK` requests, that (if you open the documentation with Firefox) this request will not work if your webserver is nginx.