This has a separate enabling option channel::channel_target_change.
It applies to PRIVMSG, NOTICE and TOPIC by unvoiced unopped non-opers.
The same slots are used for channels and users.
This way, the information remains valid after a split.
For clients on TS5 servers, the nick is used; this is
not much of a problem because these are on pseudoservers
and not assumed to change nick much at all.
