association mapping updates rows every time

[Mike Bayer]

if you have an association mapping, the DependencyProcessor puts the instances into the UOWTransaction to be updated regardless of if they were marked as changed.

might want to move the "association mapping" logic into the unit of work, where it will just detect "pending instance/deleted instance with same PK" and just convert the INSERT/DELETE into a single UPDATE, which would be a more general solution.

[Mike Bayer]

took down AssociationDP into just a OneToManyDP that enforces delete/delete-orphan cascade. works great...hooray ! changeset:1903