ACG::Geometry::triangleIntersection has way too large epsilon on the

area of the triangle causing it to find no intersections in settings
with moderately small triangles.

Choosing an epsilon relative to the underlying floating point type now.

Fixes #84.

libs_required/ACG/Geometry/Algorithms.cc

@@ -1337,8 +1337,10 @@ triangleIntersection( const Vec&  _o,
     //if determinant is near zero, the ray lies in plane of triangle
     det = edge1 | pvec;
 
-    if (det > -0.000001 && det < 0.000001)
+    static const typename Vec::value_type EPSILON = std::numeric_limits<typename Vec::value_type>::epsilon() * 1e2;
+    if (det > -EPSILON && det < EPSILON) {
         return false;
+    }
     inv_det = typename Vec::value_type(1.0) / det;
 
     //calculate distance from vert0 to ray origin