More fixes for optional activity - the previous fix didn't work for optional activities that were in more than one column (yes 1.0.2 supported a "matrix" layout) and the y co-ord for the overall optional activity isn't reliable - have to take it from the child activities.
Sort the child activities in an optional activity based on the y co-ordinate, rather than the order in the sequence. This seems to give an order that matches to 1.0.2 better than the order in the sequence.