add per-mapper dependencies even if no detected state change on relationship

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# randomize sets
from sqlalchemy.orm import unitofwork, session, mapper, dependency
from sqlalchemy import topological
from sqlalchemy.test.util import RandomSet
topological.set = unitofwork.set = session.set = mapper.set = dependency.set = RandomSet
##########

from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import relationship, Session
from sqlalchemy.schema import Column, ForeignKey
from sqlalchemy.types import Integer

engine = create_engine('postgresql://scott:tiger@localhost/test', echo=True)

Model = declarative_base()

class Parent(Model):
   __tablename__ = 'parents'

   id = Column(Integer, primary_key=True)


class Child(Model):
   __tablename__ = 'children'

   id = Column(Integer, primary_key=True)
   parent_id = Column(Integer, ForeignKey('parents.id'),
                      nullable=False)
   parent = relationship('Parent')


Model.metadata.create_all(engine)

parent = Parent()
children = [Child(parent=parent)](Child(parent=parent),)

session = Session(engine)

try:
   session.add_all(children)
   session.add(parent)
   session.commit()


   for child in children:
       session.delete(child)
   session.delete(parent)
   session.commit()
finally:
   Model.metadata.drop_all(engine)
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