through the test again. Adding helpful comments in line-drawing routines.
Swapping the constant color polygon fill with the color-interpolated polygon
fill, putting the constant color up top. Simple code first. Followed the same
strategy with line-drawing code: have already put the single color line-draw
first. Final read-through. Looks good. I want to add some test scenarios
to Donut, then release new versions of grafx and grafx_3d.
