Timeout on `close`, then force unilateral.

[ZmnSCPxj]

I propose we add a timeout on close command, and, if not complete bilateral negotiation by timeout, force a unilateral close.

I think this also implicitly includes dev-fail functionality: set the timeout to 0 and you will immediately try a forced unilateral close.

(dev-fail seems too useful for getting things unstuck to be a dev-only command).