patch applied (packages/base): In docs for unsafeCoerce, point to unsafeCoerce#

[Simon Marlow]

Simon Peyton Jones wrote:
> Mon Apr 21 08:22:51 PDT 2008  simonpj at microsoft.com
>   * In docs for unsafeCoerce, point to unsafeCoerce#
> 
>     M ./Unsafe/Coerce.hs +3

I think we want to say "GHC only" here - Unsafe.Coerce.coerce is the 
portable version.

Cheers,
	Simon