Add SID related calls to the NSS responder
    
    The patch adds 4 new calls to the NSS responder:
    - SSS_NSS_GETSIDBYNAME
    - SSS_NSS_GETSIDBYID
    - SSS_NSS_GETNAMEBYSID
    - SSS_NSS_GETIDBYSID
    to either return the SIDs of the requested object or map the SID to the
    name or the POSIX ID of the related object.