I have written a small patch for nginx that allows the use of the
X-Forwarded-Host instead of the Host header.

The rationale is that some hosting companies that use Apache as main web
server do not set the correct Host header in the proxied request.

With this patch nginx behind a proxy server is able to properly do
virtual hosting.

The patch adds a new configuration directive use_x_forwarded_host in
the main configuration context.
This directive is a flag and its default value is off.

I would like to receive a review for this patch.

Thanks Manlio P.