- A tweak to the unit of work causes it to order

- A tweak to the unit of work causes it to order
the flush along relationship() dependencies even if
the given objects don't have any inter-attribute
references in memory, which was the behavior in
0.5 and earlier, so a flush of Parent/Child with
only foreign key/primary key set will succeed.
This while still maintaining 0.6 and above's not
generating a ton of useless internal dependency
structures within the flush that don't correspond
to state actually within the current flush.
[ticket:2082]