Updated default shuffling behavior for training and cross-validation

This pull request implements the solution proposed in #190 
Yeah, a warning would be better, but it should only be printed if `shuffle` is set to false but `grid_search` is true.

Also, KFold has a `shuffle` arg.  Should we be using that?  I think we may have already considered this.
(http://scikit-learn.org/stable/modules/generated/sklearn.cross_validation.KFold.html#sklearn.cross_validation.KFold)