Bug 706179 - DS can not restart after create a new objectClass has entryusn attribute
    
    https://bugzilla.redhat.com/show_bug.cgi?id=706179
    
    Description: entryusn used to be dynamically added in the backend
    init, which occurred after the schema initialization.  And it made
    the server's start-up fail when an objectclass contains entryusn
    as its attribute type.  This patch adds entryusn to the schema
    file.