Function settle_mention 

pub fn settle_mention(p: &mut Pending, f: &Facts) -> bool

A mention is a reason a thread keeps too, so a thread that began with one says so on every later update. On a pull request spar reviewed, or an issue whose pull request it reviewed, only a mention made since that review asks for a second look; any other is only something happening on a thread the viewer is part of. True when it was.