Known only to force +r

[NaNgets]

This change makes sure that when known only mode is set, only registered users may join the channel, to avoid them being banned upon first join if not registered.

[retropc]

I agree with the idea, however there's the problem of restoring the channel modes to what they were before after unsetting +k

[retropc]

alter cs_docheckchanmodes to check for the channel flag + set the mode, instead of altering the user's chanmodes selection