Leaking existance of private channels

[marcog]

14:04 < netdog> Spinach: seen imesias
14:04 < Spinach> netdog: imesias was last seen 1 year, 4 months, 29 days, 6 hours, 10 minutes and 47 seconds ago in [redacted] on atrum [2009-10-29 07:53:29 SAST]

This response leaked the existence of the private channel [redacted] on atrum in a public channel. The feed plugin potentially does this too, listing feed announcements and the corresponding channels.

We should probably detect private channels and either redact the channel name or keep activity in private channels entirely away from other channels.