QAbstractItemModel: When calling canFetchMore() what kind of scroll on the view just happened

Inform the model when calling canFetchMore() what kind of scroll on the view just happened. This would mean that in the case of a model like the SQL ones, the rows don't need to be refetched if horizontal scrolling occurs. But at the moment if canFetchMore() is called, it will assume that it wants more rows, not more column type data. This would enable the model to be smarter about when it fetches data.