INT 21 - LANtastic v4.0+ - SCHEDULE SERVER SHUTDOWN
        AX = 5FC8h
        ES:DI -> ASCIZ server name in form "\\machine"
        DS:SI -> ASCIZ reason string (80 characters)
        CX = number of minutes until shutdown (0 = immediate)
        DX = option flags (see below)
Return: CF clear if successful
        CF set on error
            AX = error code
SeeAlso: AX=5FC9h

Bitfields for option flags:
 bit 0  auto reboot
 bit 1  do not notify users
 bit 2  halt after shutdown
 bit 3  shutdown due to power fail (used by UPS)
 bits 4-7       reserved
 bits 8-14      user definable
 bit 15 reserved

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