Use scheme-relative (aka protocol-relative) URLs for redirects

This ensures that quark really does not care if the incoming connection
is plain HTTP or relayed TLS-traffic from a proxy or tunnel. Depending
on the previous negotiation, the client will make the right decision on
which scheme to use in a given context.

http.c

@@ -391,7 +391,7 @@ http_send_response(int fd, struct request *r)
 		            "HTTP/1.1 %d %s\r\n"
 		            "Date: %s\r\n"
 		            "Connection: close\r\n"
-		            "Location: http://%s%s%s%s%s%s\r\n"
+		            "Location: //%s%s%s%s%s%s\r\n"
 		            "\r\n",
 		            S_MOVED_PERMANENTLY,
 		            status_str[S_MOVED_PERMANENTLY],