INT 62 u - FGDRIVER v3.03 - "FG_WAITVR" - ENABLE/DISABLE VERTICAL RETRACE WAIT
        AX = 00AEh
        BX = new state (0000h disabled, 0001h enabled)
Note:   For FGDRIVER v1.10, this function was unused; "FG_WAITVR" did not
          exist yet

.