SVG plugin additions

[micheus]

Nice.

There was still a point at the end of the generated path that was similar to the first point before the path closing command. It could be that key_exists might have been caused by that.

Yeah. Probably it was the cause.
I think I already face that before in a similar situation which I was trying to insert a coordinate twice in a gb_trees (I was using coordinate as index). In that case it was easy because the problem was happening in my code (not in Wings3D's module) and I just checked it before to insert.