Align ordering of rolluprecursive with simple grouping

[HeikoTheissen]

groupby with rolluprecursive should order its output set in the same way as groupby with simple grouping:

• No order is defined between instances from different portions $R(x_i)$ and $R(x_j)$ (unless the fourth parameter ends with traverse).
• The order of occurrences from each $R(x_i)$ remains the same.