Check for duplicated DN on user creation
Implement _preModifyUser on LdapUserBase
Change user modification hook from _modifyUser to _preModifyUser

Throw DataExists exception if the user try to rename a user on a
container and already exists
set proper dependency
Merge branch '3.2' into scabrero/samba-improve-user-creation-errors

Conflicts:
	main/samba/ChangeLog
	main/users/ChangeLog
Merge branch '3.2' into scabrero/samba-improve-user-creation-errors

Conflicts:
	main/samba/ChangeLog
Merge pull request #892 from Zentyal/scabrero/samba-improve-user-creation-errors

Scabrero/samba improve user creation errors