- Handle another specific case where there the JOIN 
  never had a query plan, but had multiple join->cleanup(full=true) calls
- The idea that there can only be MAX_TABLES subuqeries/unions was 
  wrong. Switch QPF_query to using a Dynamic_array.
  = make Dynamic_array template support size growth. its underlying
    DYNAMIC_ARRAY supports it. (this part will need more polishing)