Import agg 2.5 from http://www.antigrain.com/
Fix non-terminating loop conditions when len=1

-   while(abs(sx - lp.x1) + abs(sy - lp.y1) > lp2.len)
+   while(abs(sx - lp.x1) + abs(sy - lp.y1) > 1 + lp2.len)
    {
        sx = (lp.x1 + sx) >> 1;
        sy = (lp.y1 + sy) >> 1;
    }
Cure recursion by aborting if the co-ordinates are to big to handle
Get coordinates from previous vertex if last command is path_cmd_end_poly
Make rasterizer_outline_aa ignore close_polygon when vertex count < 3
Remove VC++ 6 workaround
Implement grain-merge blending mode (GIMP)
Implement grain-extract blending mode (GIMP)
Declare multiplication and division operators as const
Add a static identity transformation
Add renderer_scanline_aa_alpha
Avoid division by zero in color-burn mode

FIXME: re-work using latest math from http://www.w3.org/TR/SVGCompositing/