Add support for auth-info and auth-info-required (STR #2268)

Add support for auth-info and auth-info-required (STR #2268)

TODO: Directory services support, reject jobs that need auth-info
but don't have the right stuff.

backend/ipp.c:
    - password_cb(): Send ATTR: message to specify the authentication
      that is required.

scheduler/classes.c:
    - cupsdLoadAllClasses(): Load AuthInfoRequired.
    - cupsdSaveAllClasses(): Save AuthInfoRequired.

scheduler/ipp.c:
    - add_class(): Save auth-info-required data.
    - add_job(): Pass auth-info data.
    - add_printer(): Save auth-info-required data.
    - authenticate_job(): Pass auth-info data.
    - save_auth_info(): Save auth-info data.

scheduler/job.c:
    - cupsdUpdateJob(): Process ATTR: messages for auth-info-required.

scheduler/printers.c:
    - cupsdLoadAllPrinters(): Load AuthInfoRequired.
    - cupsdSaveAllPrinters(): Save AuthInfoRequired.
    - cupsdSetAuthInfoRequired(): Added.
    - cupsdSetPrinterAttrs(): Add auth-info-required.

scheduler/printers.h:
    - Add auth_info_required and num_auth_info_required to
      cupsd_printer_t structure.
    - Add cupsdSetAuthInfoRequired attribute.

git-svn-id: svn+ssh://src.apple.com/svn/cups/cups.org/trunk@6318 7a7537e8-13f0-0310-91df-b6672ffda945