I am in the process of rewriting all of the render code but as far as I know, the frustum pulls the clip distance from this line in init.cpp:
Code:
gluPerspective(75.0f,(GLfloat)width/(GLfloat)height, 0.1f , 10000.0f);
The last value in that command represents the furthest view able region.Again, this will be changed when shader rendering is in place. Hope this helps though.