Properly export all lua-facing functions and use those for initialization (love.cpp no longer explicitly mentions implementations)

src/modules/physics/box2d/wrap_RopeJoint.h

@@ -34,7 +34,7 @@ namespace box2d
 {
 	RopeJoint * luax_checkropejoint(lua_State * L, int idx);
 	int w_RopeJoint_getMaxLength(lua_State * L);
-	int luaopen_ropejoint(lua_State * L);
+	extern "C" int luaopen_ropejoint(lua_State * L);
 
 } // box2d
 } // physics