fix build failure against ghc-HEAD (die clast, FlexibleContexts)

The name clash failure is easy:
>    Ambiguous occurrence ‘die’
>    It could refer to either ‘Main.die’, defined at src/Main.lhs:291:3
>                          or ‘System.Exit.die’,
>                             imported from ‘System.Exit’ at src/Main.lhs:28:3-20

The type inference constraints with language extensions are
more tight now:
http://permalink.gmane.org/gmane.comp.lang.haskell.glasgow.user/24612

Signed-off-by: Sergei Trofimovich <slyfox@gentoo.org>
Merge pull request #21 from trofi/master

fix build failure against ghc-HEAD (die clast, FlexibleContexts)