Trac Ticket #412 - memberof performance enhancement
    
    https://fedorahosted.org/389/ticket/412
    
    Fix description:
    memberof.c: replaced DN strings with Slapi_DN and set the
    normalized info to Slapi_Value flags.  It reduces the number
    of slaip_dn_normalize_ext call by ~25%.
    
    attr.c, slapi-plugin.h: introduced a new API slapi_attr_
    value_cmp_ext which takes Slapi_Value instead of struct
    berval.  By replacing with Slapi_Value, the value flag
    (e.g., normalized info) can be passed to the syntax plugin.
    
    value.c: changed slapi_value_compare to call slapi_attr_
    value_cmp_ext instead of slapi_attr_value_cmp.
    (cherry picked from commit 6a21e8e9be90de76549b8fb37dc744ca48234e00)