- A new Base.getMountedObject method allow to access to parent object in the
  mounted storage so that it is possible to migrate their class persistently.
  A common pattern for modules in different Data.fs would be:
    real_module = portal.mounted_module.getMountedObject()
    real_module.getParentValue().migrateToPortalTypeClass()

- Make it possible to manage mount points in unit tests.

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@44781 20353a03-c40f-0410-a6d1-a30d3c3de9de