Duplicate UID in seperate organisation units

At the moment it's not possible to create same UID in seperate organisation unit, but it should be possible, there is no reason why FD block it. Perhaps it could be a problem with memberships if not rfc2307bis is used, but with rfc2307bis it should work.

(from redmine: issue id 350, created on 2011-07-09, closed on 2014-09-03)