Build type information on first use (load-time), instead of using a hardcoded list

--HG--
branch : dynamiccore2

src/modules/physics/box2d/MouseJoint.cpp

@@ -32,6 +32,8 @@ namespace physics
 namespace box2d
 {
 
+love::Type MouseJoint::type(&Joint::type);
+
 MouseJoint::MouseJoint(Body *body1, float x, float y)
 	: Joint(body1)
 	, joint(NULL)