INT 31 P - DPMI 0.9+ - DISCARD PAGE CONTENTS
        AX = 0703h
        BX:CX = starting linear address
        SI:DI = number of bytes to mark as discarded
Return: CF clear if successful
        CF set on error
            AX = error code (DPMI 1.0+) (8025h) (see AX=0000h)
Notes:  this function is advisory, and may be ignored by DPMI implementations
        partial pages will not be discarded
SeeAlso: AX=0702h