resurrect the "add double" method of the setup code
emulation fix: instead of taking the "start hretrace" param directly per
line, average it instead (since CRTs have inertia in their raster) and
use the averaged value to displace the scanline. added code to both
adjust video ram address and displace the scanline for finer
displacement. This makes the effect in "copper" by Surprise! productions
much better looking, and probably closer to how a VGA monitor would deal
with it.