2. Make domtree printing print dfin/dfout #'s
3. Fix the Transforms/LoopSimplify/2004-04-13-LoopSimplifyUpdateDomFrontier.ll failure from last night (in DominanceFrontier::splitBlock).

w.r.t. #3, my patches last night happened to expose the bug, but this 
has been broken since Owen's r35839 patch to LoopSimplify.  The code
was subsequently moved over from LoopSimplify into Dominators, carrying
the latent bug.  Fun stuff.

llvm-svn: 40858