- establish a consistent pattern of behavior along o2m, m2m, and m2o relationships

- establish a consistent pattern of behavior along o2m, m2m, and m2o relationships
when "save-update" cascade is disabled, or the target object is otherwise not
present in the session, and collection/scalar changes have taken place.  A warning
is emitted describing the type of operation, the target reference, and the relationship
description, stating that the operation will not take place.  The operation then doesn't
take place.   [ticket:1973]
- clean up test_cascade a little bit, remove cruft