issue #2771:  add tag and enable functions to physics classes
Merge branch 'develop' of https://github.com/cocos2d/cocos2d-x into iss2771_physical
issue #2771:  refactor PhysicsTest
issue #2771:  move _physicsBody from sprite to node
issue #2771:  separate the PhysicsBody and the PhysicsShape.
issue #2771:  fix some bugs in PhysicsShape
issue #2771:  let PhysicsShape::create doesn't need to pass the PhysicsBody
issue #2771:  add PhysicsMaterial
issue #2771:  Let the sprites added to SpriteBatchNode support physics.
issue #2771:  fix some compile error.
issue #2771:  add #ifdef CC_USE_PHYSICS to CC_SAFE_DELETE(_physicsWorld)
issue #2771:  delete #define RAND_MAX in PhysicsTest.cpp(already defined in stdlib.h)
Merge pull request #3916 from boyu0/iss2771_physical

[ci skip]issue 2771: physical