Give a more appropriate "I'm not an HTTP proxy" message when we get an HTTP request on the control port
Right now if you accidentally configure your applications to use the control port as an HTTP proxy or a SOCKS proxy, the applications don't get any useful feedback, and the log messages aren't too helpful. They might tell you that something weird happened, but they won't say what.
When possible, then, the control port should detect HTTP and SOCKS requests. It should respond to HTTP request with a "Tor isn't an HTTP Proxy" message to the HTTP request-maker, and should in both cases log the fact that the control port was used as the wrong kind of proxy.