menuArgs breaks compilation on GHC < 7.10 because it uses fmap but
only has a MonadIO constraint.
Functor was not a superclass of Monad until GHC 7.10.
MonadIO is compatible with xfork which prevents dmenu prompts from
freezing XMonad.
Without xfork, if I try to give focus to another window while dmenu is
waiting, XMonad freezes until I kill dmenu in virtual terminal or ssh
session.
This should not cause any working configs to stop working, because IO is an instance of MonadIO, and because complete configs will pin down the type of the call to IO. Note that XMonad.Config.Arossato is not a complete config, and so it needed some tweaks; with a main function, this should not be a problem.
