HTTPS check fails in environments providing HTTP_X_FORWARDED_PROTOCOL

As some proxies seem to provide HTTP_X_FORWARDED_PROTOCOL instead of HTTP_X_FORWARDED_PROTO, cdn_request_is_https() should check them both:

cdn.module:

@@ -702,6 +702,12 @@
            isset($_SERVER['HTTP_X_FORWARDED_PROTO'])
            &&
            $_SERVER['HTTP_X_FORWARDED_PROTO'] == 'https'
+         )
+         ||
+         (
+           isset($_SERVER['HTTP_X_FORWARDED_PROTOCOL'])
+           &&
+           $_SERVER['HTTP_X_FORWARDED_PROTOCOL'] == 'https'
          );
 }