AbstractRegistry wraps the definition decorators into a caching wrapper. Sometimes, e.g. when we need to de-register a DefinitionProvider, we need to compare some instance of a decorator (not wrapped) to the one from the registry (wrapped one). However, the CachingDefinitionDecorator won't recognise a DefinitionDecorator of any other type as equal. This needs to be somehow improved and made more transparent for the user.