In the migration framework, fix queries for Archetype objects, where only
  interfaces are used to skip brains with no or Dexterity meta_type. In some
  cases Dexterity and Archetype objects might provide the same marker
  interfaces.
 Add a ICustomMigrator interface to the migration framework, which can be used
  to register custom migrator adapters. This can be useful to add custom
  migrators to more than one or all content types. For example for
  schemaextenders, which are registered on a interface, which is provided by
  several content types.