output error code when xmonad.hs compile fails without any error output
output error code when xmonad.hs compile fails without any error output


Currently if there is no ghc on the path say for some reason,
xmonad.error is empty.  This patch makes
it output the exitcode code when the compile process fails
without any error output.  (It might be easier just to spawn
a shell to get "ghc: command not found" output for free.)

ohlus/xmonad,pjones/xmonad-test,ericssmith/xmonad,xmonad/xmonad