darcs patch: make stage1 type-class-extension free

[Isaac Dupree]

Simon Peyton-Jones wrote:
> Thanks Isaac, that's great. I've simplified your last two patches quite a bit,
 > and pushed the lot.

Thanks! for the GenIface one, you understand what the data structure is 
doing enough that you were able to change it;

and for DebugNodes, hmm.  You may have reduced it so that only 
MultiParamTypeClasses is needed (I'll have to check with 6.8 -- I don't 
fully understand what the instance rules for MultiParamTypeClasses are 
supposed to be normally).  And... all current compilers support 
MultiParamTypeClasses? (
http://hackage.haskell.org/trac/haskell-prime/wiki/HaskellExtensions 
claims neither nhc nor jhc do?) although it looks like neither of the 
post-modification DebugNodes instances actually require 
FlexibleInstances, as far as I can tell from the haskell-prime wiki...

I'll save any more concern about that until later after I've fixed the 
other more blatant portability problems.

~Isaac