update Request::referer() to correctly identify local urls which contain a full url string

`\lithium\net\http\Request::referer()` would be much more useful if it could identify `HTTP_REFERER` values which contain `HTTP_HOST` when filtering for local urls.

AFAIK, `HTTP_REFERER` is almost never set to an absolute path sans-host, so I don't see how the current implementation of the $local parameter is useful.

This method is useful to me on a particular project of mine where I wanted to return a user to the referring page after login (say due to a 403 response), but only when the referrer was local.