Fix pattern overlap warning with GHC-7.8 and GHC-7.10
Fix pattern overlap warning with GHC-7.8 and GHC-7.10

`show (ErrorCall x) = x`, so the error message is as before.

AndrewRademacher/stack,sjakobi/stack,Heather/stack,AndrewRademacher/stack,anton-dessiatov/stack,Fuuzetsu/stack,MichielDerhaeg/stack,AndreasPK/stack,deech/stack,Blaisorblade/stack,martin-kolinek/stack,mrkkrp/stack,MichielDerhaeg/stack,Fuuzetsu/stack,juhp/stack,martin-kolinek/stack,sjakobi/stack,deech/stack,juhp/stack,Heather/stack,Blaisorblade/stack,AndreasPK/stack,anton-dessiatov/stack,mrkkrp/stack