Slight doc typos

[Simon Marlow]

> Section 7.4 of the User Guide (or doc source
> ghc/docs/user_guide/glasgow_exts.sgml) references "Haskell 
> 1.4" several
> times when "Haskell 98" would perhaps be more appropriate.
> 
> Also, section 7.4.10 ("Arbitrary-rank polymorphism", same sgml source)
> has an example with functions f1, g1, f2, g2 and f3, but a few
> paragraphs later a non-existent g3 is mentioned twice.

Thanks; fixed.

Simon