Requests through a sandbox's web proxy no longer wait 40 ms on responses

The sandbox's web proxy relay (127.0.0.1:10800) and guest-egress.py forward now set TCP_NODELAY on the program's connection. Previously the kernel held the last segment of any response longer than one segment until the program acknowledged the one before, and most clients delay that acknowledgement by 40 ms. A call to Runtime's API from a sandbox that returns more than about 1.4 KB (creating, pausing or waking a sandbox, reading a file, listing sandboxes) completes about 40 ms sooner, as does any other request made through the proxy. A sandbox uses the new relay from its next boot, or from the wake after its next pause. The transparent relay, used by programs that ignore HTTPS_PROXY, gets the same change with the next base image.