wrapper: explicitly warn about unknown options
wrapper: explicitly warn about unknown options

Reported as item #1 here:

    https://github.com/ChrisJohnsen/tmux-MacOSX-pasteboard/issues/13

lembacon/tmux-MacOSX-pasteboard,ChrisJohnsen/tmux-MacOSX-pasteboard,bradparks/tmux-MacOSX-pasteboard,tjt263/tmux-MacOSX-pasteboard