[TYPO3-mvc] Cloning Model and add to repository

[Sebastian Kurfürst]

Hey,

definitely the error message should be improved.

> But that's what he tried to do. He cloned an old object to get a new one. He already assumed that it
> had no connection to the repositry, so he added it. That's where Extbase choked. Either a bug or he
> did something else and the error message wasn't helpful enough.
The problem is that the object still needs the repository metadata
(read: the "original" UID) inside, as we need it if somebody does
$myRepository->update($object), which is the most common use-case.

Greets,
Sebastian