PATCH: implementation for TH PprLib.hs punctuate function

[Duncan Coutts]

Hi,

I noticed that the 6.3 version of the PprLib.hs is not fully implemented
so pretty printing some things calls Prelude.undefined.

With the other monadic version of the HughesPJ combinators you can just
wrap them using liftM or similar but that doesn't work out so well for
punctuate as the type won't be right. So I've basically unfolded the
definition of punctuate and then added in the monadic bits.

Attached patch typechecks but I've not rebuilt yet so I've not tested it
(but it looks right :-) ).

Duncan
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