INT 10H 12H BL=36H: Enable/Disable Screen Refresh

                                                          Compatibility: VGA 
 Expects: AH    12H
          BL    36H
          AL    setting: 00H enable refresh
                         01H disable refresh
 Returns: AH    12H if a valid value was passed in AL
    Info: This modifies bit 5 of the VGA's Sequencer Clocking Mode Register
          (see VGA I/O Ports).

          You can draw complex graphics faster while refresh is disabled
          (it avoids some enforced wait states).  Be sure to re-enable
          refresh when finished updating video memory.

See Also: INT 10H 12H (EGA/VGA Special Functions/Alternate Select)
          INT 10H: Video Services
          EGA/VGA Data Areas