Bug 619633 - Make attribute uniqueness obey requiredObjectClass
    
    The attribute uniqueness plug-in currently does not enforce the
    requiredObjectClass setting properly.  The plug-in checks that the
    entry being modified meets the requiredObjectClass setting, but it
    does not check if the potential conflicts in the database meet this
    requirement as well.
    
    This patch changes the behavior to check that both the target and
    potential conflicting entries meet the requiredObjectClass setting.