pc.close() almost stops transceivers fully.

[jan-ivar]

pc.close() rolls its own version of stop transceiver that is almost—but not quite—identical to tc.stop().

The difference looks accidental: It forgets to set [[Receptive]]=false and [[CurrentDirection]]=null.

These somewhat recent additions look like they got out of sync.

We probably want to rewrite this to reference a common algorithm.