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

[Malcolm Wallace]

Simon Peyton-Jones <simonpj at microsoft.com> wrote:

> If this is Haddock'd for NHC, the link to unsafeCoerce# will yield an
> error message, I suppose, even if we precede with "In GHC,
> 'unsafeCoerce' is just..."
> 
> So I'm still not sure what to do.  For now it's as above.  Perhaps
> someone who knows how it should come out on, say nhc or hugs, can
> modify it appropriately?

I have added some text to clarify that the safety depends on which
compiler you are using, documented roughly what is safe in nhc98, and
kept the forward link to GHC.Base.unsafeCoerce#.  Maybe Hugs and jhc
experts could add some text about those implementations too.

Regards,
    Malcolm