relationships no longer compile against the "selectable" mapper (i.e. the polymorphic...

relationships no longer compile against the "selectable" mapper (i.e. the polymorphic mapper).  join conditions, foreign keys etc. are configured against the actual mappers used in the relationship in all cases.  the lazy and eager loaders in turn "adapt" their lazy/eager clauses to that of the "selectable" mapper if one is present.  this is because the join conditions between the mapper's base tables are *far* easier to work with and detect direction etc. compared to an enormous polymorphic union; dealing with the polymorphic union is pushed further out into select query construction.