Mesa 7.3.1 software rasterizer snapping cause holes

I'm trying to software render Humus softshadows http://www.humus.name/index.php?page=3D&ID=51
And i'm getting holes in the wood and in other places in the scene.
The holes are created because of triangle snapping with 4 bits of accuracy and this creates gaps in the geomatry, is it possible to increase the SUB_PIXEL_BITS and solve this problem?