export predicted-ports via control interface
In #4718 (closed) Mike made Torbutton launch a new request every 12 hours.
This basically torpedos Tor's "go idle and don't build circuits or fetch descriptors when no requests lately" code.
We should export "whether we're dormant" via a getinfo.
I set the milestone to 0.2.2 since I think Mike is expecting his feature to get into a TBB 2.2 release.