data race on srv.Server.ConnState = nil

[jeffallen]

As seen in dedis/onet#359, there's a data race between the Go stdlib HTTP server and Graceful on shutdown.

It looks like http.Server.ConnState is only safe to be set before the server is started.

What if you removed the ConnState = nil? If it must not be called any more, then what about adding a bool to type Server called something like "ignoreConnStatus"?