switch back to inlineCallbacks???
track living clients, avoid responses accumulating

When any Requester is connected, it will register itself
in an "active clients" set ("txscale.clients") and the server
will only push to a client response list if the client is registered
in the txscale.clients set.

also work around a race condition in crapc.py which would previously
cause the crapc client to try perform more protocol actions even
after the protocol was disconnected.
don't look, I'm writing tests for untested code again