Perform case-insensitive searches for principals on TGS requests
    
    We want to always resolve TGS requests even if the user mistakenly sends a
    request for a service ticket where the fqdn part contain upper case letters.
    
    The actual implementation follows hints set by KDC. When AP_REQ is done, KDC
    sets KRB5_FLAG_ALIAS_OK and we obey it when looking for principals on TGS requests.
    
    https://fedorahosted.org/freeipa/ticket/1577