- after ht_thetajoin, the iter numbers were mapped to the forward scope   in a way that did not guarantee preserving their order.
- after ht_thetajoin, the iter numbers were mapped to the forward scope
  in a way that did not guarantee preserving their order.

  iter not being ordered in our code causes havoc at random later points.
  (in this case, a merged_union complained about it)

zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb,zyzyis/monetdb