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

[Simon Peyton-Jones]

| > Ah, good point. How do we say "GHC only" in documentation?  In words?  Or with #ifdef?
|
| It's better to have the same documentation for everyone, with words about
| what's implementation-specific.

The words in Unsafe.Coerce are these:

-- 'unsafeCoerce' is just a trivial wrapper for 'unsafeCoerce#';
-- see the latter for important documentation about correct usage.

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?

Simon