code: function ActionManager () {
      ActionManager.superclass.constructor.call(this)
  
      Scheduler.sharedScheduler.scheduleUpdate({target: this, priority: 0, paused: false})
      this.targets = []
  }
docs: @class
  A singleton that manages all the actions. Normally you
  won't need to use this singleton directly. 99% of the cases you will use the
  cocos.nodes.Node interface, which uses this singleton. But there are some cases where
  you might need to use this singleton. Examples:
  
  * When you want to run an action where the target is different from a cocos.nodes.Node
  * When you want to pause / resume the actions
  
  @memberOf cocos
  @singleton