Fix warnings in IntSet.hs.
Fix warnings in IntSet.hs.

Mostly usual shadowing issues.

hvr/containers,iu-parfunc/containers,ekmett/containers,iu-parfunc/containers,Zigazou/containers,ekmett/containers,Zigazou/containers,hvr/containers,iu-parfunc/containers,shockkolate/containers,hvr/containers,shockkolate/containers,Zigazou/containers,shockkolate/containers,meiersi/psqueues-old,ekmett/containers