[BUGFIX release] Fix finishChains

Fix `finishChains` for all chains that reference an obj not just the ones rooted at that object.
As far as I know, this isn't the slow case (chainWatchers are always simple objects and copied), and I'm hesitant to make this change as part of this pull, since none of the other code in `chains.js` is using keys over for/in, I'd rather see the switch to keys() uniformly in chains with some cross browser perf data.