[project @ 2005-07-11 09:48:57 by simonpj]

[project @ 2005-07-11 09:48:57 by simonpj]
Fix a bug in the renamer for parallel list comprehensions
	MERGE TO STABLE

It's surprinsingly tricky to combine
  a) The parallel scopes for par-list-comps
with
  b) The general form of the renamer types, whereby
     scoped constructs work like
	 rnPat :: Pat -> RnM (thing,FreeVars)
	       -> RnM ((Pat,thing), FreeVars)
     This general shape neatly allows rnPat to
     extend the envt, report unused variables from
     the 'thing' inside, and return the correct set
     of free variables

But combining (a) and (b) is tricky, and was plain wrong before.