fixed manifold exploration for point light sources and cylinders (cardioid test scene works again..)

src/libbidir/manifold.cpp

@@ -915,7 +915,7 @@ Float SpecularManifold::G(const Path &path, int a, int b) {
 
 	SimpleVertex &last = m_vertices[m_vertices.size()-1];
 	const PathVertex *vb = path.vertex(b);
-	if (vb->isMediumInteraction()) {
+	if (!vb->isOnSurface()) {
 		last.n = Vector(path.edge(a < b ? (b-1) : b)->d);
 	} else {
 		last.n = vb->getShadingNormal();

src/shapes/cylinder.cpp

@@ -495,7 +495,7 @@ public:
 
 	void getNormalDerivative(const Intersection &its,
 			Vector &dndu, Vector &dndv, bool shadingFrame) const {
-		dndu = its.dpdu / m_radius;
+		dndu = its.dpdu / (m_radius * m_flipNormals ? -1 : 1);
 		dndv = Vector(0.0f);
 	}