Proposal: Performance improvements for Data.Set

[Isaac Dupree]

+1 to the Set, Map, IntMap, etc., performance improvements.  The style 
consistency is probably a good concomitant effect.  Testsuite and 
benchmark make sense in concept too (I haven't looked at the code, I 
trust that it's fine).  Good job!

Antoine's "Is this sort of optimization specific to the way GHC compiles 
things, or will other compilers likely either benefit or not care?" is 
an interesting question that I'd be curious to hear about. (does 
Criterion work on non-GHC?). but that in my judgment shouldn't delay 
these particular patches.

-Isaac