- lazy loader can now handle a join condition where the "bound"

- lazy loader can now handle a join condition where the "bound"
column (i.e. the one that gets the parent id sent as a bind
parameter) appears more than once in the join condition.
Specifically this allows the common task of a relation()
which contains a parent-correlated subquery, such as "select
only the most recent child item". [ticket:946]
- col_is_part_of_mappings made more strict, seems to be OK
with tests
- memusage will dump out the size list in an assertion fail