Constraints can override their own number of solver iterations (either more or less than the default) or leave it default (-1)

Bump version to 2.80

Demos/SerializeDemo/SerializeDemo.h

@@ -64,6 +64,8 @@ class SerializeDemo : public PlatformDemoApplication
 
 	void	exitPhysics();
 
+	virtual void keyboardCallback(unsigned char key, int x, int y);
+
 	virtual void clientMoveAndDisplay();
 
 	virtual void displayCallback();