Allow anonymous access to be disabled.
    
    This adds a new config switch (nsslapd-allow-anonymous-access) that
    allows one to restrict all anonymous access.  When this is enabled,
    the connection displatch code will only allow BIND operations through
    for an unauthenticated user.  The BIND code will only allow the
    operation through if it's not an anonymous or unauthenticated BIND.