tmux: update for compatibility with tmux master branch
tmux: update for compatibility with tmux master branch

See commit 76d6d3641f271be1756e41494960d96714e7ee58 in the tmux repo.

wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent