- unit-of-work does a better check for "orphaned" objects that are

- unit-of-work does a better check for "orphaned" objects that are
part of a "delete-orphan" cascade, for certain conditions where the
parent isnt available to cascade from.
- it is now invalid to declare a self-referential relationship with
"delete-orphan" (as the abovementioned check would make them impossible
to save)
- improved the check for objects being part of a session when the
unit of work seeks to flush() them as part of a relationship..