Do not flag a tab for a channel when a nick-change, join, leave etc. occurs
if that same event already has been shown in the currently active channel.
I and a user named Tom both sit in #a and #b, and #a is the currently
Tom changes /nick to Tom|away.
In X-chat today, #b's channel tab would be flagged red.
I find that unnecessary, because I have already seen Tom's nick change in
the current channel.