Fix missing import in HscMain

[Ian Lynagh]

Hi David,

After this patch:

> commit 54b7afc5b56406459dc41b7e4e91f8d062e741ba
> Author: David Terei <davidterei at gmail.com>
> Date:   Thu Jan 26 01:50:44 2012 -0800
> 
>     Fix missing import in HscMain.
> 
> diff --git a/compiler/main/HscMain.hs b/compiler/main/HscMain.hs
> index e06e6fa..13d85bf 100644
> --- a/compiler/main/HscMain.hs
> +++ b/compiler/main/HscMain.hs
> @@ -145,6 +145,7 @@ import UniqSupply       ( initUs_ )
>  import Bag
>  import Exception
>  
> +import GHC.Exts
>  import Data.List
>  import Control.Monad
>  import Data.Maybe

my HEAD validate is failing with:

compiler/main/HscMain.hs:148:1:
    Warning: The import of `GHC.Exts' is redundant
               except perhaps to import instances from `GHC.Exts'
             To import instances alone, use: import GHC.Exts()

Why did you need to add the import? And what platform does it validate
on for you?


Thanks
Ian