Meansquarenormalization

Don't actually pull this yet; it just seems the best way to get a complete diff for the branch on github is to issue a pull request.  

Re: prediction vs. update.  Do you think it's possible to do this entirely by changing the sequence of weight updates rather than adjusting the value of the feature during prediction?

At the moment the cost for other predictors is that the total weight is being computed and stored in predict_data for inline_predict, but otherwise is all.training is false and/or --meansq is not enabled, there's no penalty.