[xmonad] Illegal Signature in SubLayouts module with ghc 6.8

[Don Stewart]

rupa:
> When trying to compile xmonad latest darcs under ghc 6.8.2dfsg1-1ubuntu1
> (jaunty default) I got the following error:
> 
> XMonad/Layout/SubLayouts.hs:309:16:
>  Illegal signature in pattern: LayoutMessages
>  Use -XPatternSignatures to permit it
> 
> Apparently people using 6.10 do not get this error, which went away when I
> added PatternSignatures to the LANGUAGE pragmas of the modules as suggested in
> IRC.
> 
> Just a heads up, I'm not sure what, if anything, should be done here ...

Could you send a patch?

-- Don