INT D4 - PC-MOS/386 v3.0+ - FREE NATIVE MODE MEMORY BLOCK
        AH = 12h
        ES = selector for block to free
Return: CF clear if successful
        CF set on error
            AX = error code (see INT 21/AH=59h)
SeeAlso: AH=10h,AH=11h,AH=13h,INT 38

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