add dragging className

add dragging className

Author: 淘小杰

lib/draggable.js

@@ -3,6 +3,7 @@
 /** @jsx React.DOM */
 var React = require('react/addons');
 var emptyFunction = require('react/lib/emptyFunction');
+var CX = React.addons.classSet;
 
 function createUIEvent(draggable) {
 	return {
@@ -434,12 +435,16 @@ module.exports = React.createClass({
 		if (this.state.dragging && !isNaN(this.props.zIndex)) {
 			style.zIndex = this.props.zIndex;
 		}
-
+		
+		var className = CX({
+			'react-draggable': true,
+			'react-dragging': this.state.dragging
+		});
 		// Reuse the child provided
 		// This makes it flexible to use whatever element is wanted (div, ul, etc)
 		return React.addons.cloneWithProps(React.Children.only(this.props.children), {
 			style: style,
-			className: 'react-draggable',
+			className: className,
 
 			onMouseDown: this.handleDragStart,
 			onTouchStart: function(ev){