Settle on Ord instance

[treeowl]

There are a bunch of comments on the Ord instances suggesting that it might be nice to use a different ordering. This shouldn't be a big deal, I don't think. Start by viewing the ends of each to see if they have the same key, in which case special logic is needed. Otherwise do the simple thing. Either way, use Data.Ord.Down. @twanvl, I'll be happy to do this, but only if you want it. Please let me know.