Ensure that pixels after active video are black.
Ensure that pixels after active video are black.

The driver has always *tried* to do this, but I did it wrong, such
that modes with fewer than 800 active pixels horizontal would produce
white stripes at the right edge of the video.  This made the 640-pixel
mode into a 644-pixel mode, which in turn made monitor sync unreliable.

cbiffle/m4vgalib,cbiffle/m4vgalib,cbiffle/m4vgalib,cbiffle/m4vgalib