Fix a memory leak in Set::removeAllObjects.
The set maintains a strong reference to all objects so release() should be called whenever something is removed from the set.
issue #2771: add physics files and entries.
issue #2771: add Node::_physicsBody to Node init list
issue #2771: add new line to the end of line.
issue #2771: Change _physicsBody from node to sprite. Reimplement Scene::addChild. Adjust some API.
issue #2771: Fix CI compile errors.
issue #2771: Fix CI compile errors.
issue #2771: Fix CI compile errors.
issue #2771: Add macros to control use physics engine or not
issue #2771:  Change CC_USE_PHYSICS_ENGINE to CC_USE_PHYSICS. Add some implements.
issue #2771:  Add method Scene::createWithPhysics() end Scene::initWithPhysics()
issue #2771:  Add PhysicsTest to TestCpp. Add initTest to TestScene, move Scene::init() from constructor to TestScene::initTest()
Disable log output on release build
issue #2771:  Implement the minimum set of physical API. Improve the PhysicsTest
Merge branch 'develop' of https://github.com/cocos2d/cocos2d-x into iss2771_physical
issue #2771:  Edit delegate to listener.
issue #2771:  update android.mk
issue #2771:  update project setting
issue #2771:  update vs project setting
Merge branch 'develop' of https://github.com/cocos2d/cocos2d-x into iss2771_physical