INT 15 - MultiDOS Plus - FORCE DISPLAY OUTPUT TO PHYSICAL SCREEN MEMORY
        AH = 0Bh
Notes:  sets calling task's screen pointer to actual screen memory; the pointer
          may be restored with AH=0Ch
        caller's video mode must be same as foreground task's video mode
        any text written while in the background will be saved to the
          foreground task's virtual screen when it switches to the background
        useful if a background task wants to display a message on the
          foreground screen