Adds "DrawMode_Absolute", which just splats texels straight down.

Useful for drawing into render targets, where you want to retain your
alpha channel AND the color values.

Also adds "edgeSmooth" for turning on or off polygon edge antialiasing
per material.  Often useful to turn off antialiasing when you're using
DrawMode_Absolute (since the whole point of Absolute drawing is to splat
down your values exactly as you ask, without being blended in any way.
Antialiasing just introduces blending again.)
Converting vsTexture back into a vsImage now brings the alpha channel.