added VoronoiFractureDemo, thanks to RBD

fix in infinite recursion in quickSort, exclude the pivot in each sub partition
disabled constraints don't merge simulation islands, and they don't disable collision between linked rigid bodies either.

src/BulletDynamics/Dynamics/btRigidBody.cpp

@@ -309,8 +309,9 @@ bool btRigidBody::checkCollideWithOverride(btCollisionObject* co)
 	for (int i = 0; i < m_constraintRefs.size(); ++i)
 	{
 		btTypedConstraint* c = m_constraintRefs[i];
-		if (&c->getRigidBodyA() == otherRb || &c->getRigidBodyB() == otherRb)
-			return false;
+		if (c->isEnabled())
+			if (&c->getRigidBodyA() == otherRb || &c->getRigidBodyB() == otherRb)
+				return false;
 	}
 
 	return true;