Cycles: fix some update issues with camera motion blur, and do some more work

for getting object motion blur ready.

intern/cycles/render/camera.h

@@ -103,6 +103,7 @@ public:
 	void device_free(Device *device, DeviceScene *dscene);
 
 	bool modified(const Camera& cam);
+	bool motion_modified(const Camera& cam);
 	void tag_update();
 };