[TYPO3-mvc] update an existing fe_user without editAction

[S.Korth]

This should be normal because the new object hasn't been persisted yet,
so it can't have an uid. What i think i have to do is to some kind of merge
the $existingUser with the $newUser, because the $existingUser has an 
uid of course.

I'm curious about how other would solve this ;-)

Or, if you want to persist the new object before using it: 
http://lists.typo3.org/pipermail/typo3-project-typo3v4mvc/2010-May/004745.html