pt_BR translation

This is a quick translation to Brazilian Portuguese. I haven't tested in any system and translation might be out of context (I personally use english in my systems, and latest version of django-mptt I used was v0.5.5), but it's basically there. I hope formats are ok.
I would add "já" before "foi".
Final result: O modelo %s já foi registrado.
Reason: phrases are in different times.