RSS messages need to be distinguished internally by unique identifiers.
Until the messages origin url was used as id. Since some RSS feeds deliver all messages with the same url parameter, we have to create own unique ids to distinguish the messages of a feed. Nevertheless the url of a RSS message is needed to show a link to its origin in the frontend.

For this purpose a new response parameter url was introduced. It will always be delivered for action=get if it has a value. If there is no value (internally null) the parameter will not be delivered.

As our messaging api seems not to be described in oxpedia yet but in dev-wiki i added the necessary information there.