Comment # 2 on bug 1185572 from Dirk Mueller

Thanks DimStar for tracking down the regression. I was afraid of this :( made
the patch more elaborate to handle the previous case again. 

it is really unfortunate that we decided to name the socket dir tmux/%d rather
than tmux-%d like upstream does, but since we carry the patch for almost a
decade already, I don't know how we could back out of that now without breaking
compatibility :/