Make several changes which should speed up RWR.
* Don't perform BFS to find which nodes we must consider--just consider all of them.
* Perform sanity checks along the way (RWR sum should always add to 1).
* Only random-walk to parents (up the tree), not down it.
Fix an oops.
Add renormalization code now that we've determined a sinkhole is causing the declining-rw-score-sum problem.