line rendering fixes

line rendering fixes
Get the reversed versus forward conservation lines correct. The color is
blue if the orientation of the current vertex differs from the previous
vertex, and red if they have the same oreintation. I also (hopefully)
adjusted the x position so the line points to the center of the conserved
window (adjusting to the right for forward and left for reverse compliment
sequences).

Also we discovered that you can't use both depth testing and alpha blending
at the same time, and so now the selection highlighter is hopefully alpha
blended while all the various lines are depth ordered.