code: function( id, xStore ){
  
  		Object.defineProperty(xStore, '_dispatcher', {
  			value: this
  		});
  
  		return this.register( id, xStore.callback );
  	}
docs: Register a XStore in the dispacher. XStores has a method called callback. The dispatcher
  register that function as a regular callback.
  
  @param  {String} id     The id for the store to be used in the waitFor method.
  @param  {XStore} xStore Store to register in the dispatcher
  @return {String}        The id of the callback to be used with the waitFor method.