added multi-touch support

Author: brianfay

lib/draggable.js

@@ -81,7 +81,7 @@ var dragEventFor = eventsFor.mouse;
  * get {clientX, clientY} positions of control
  * */
 function getControlPosition(e) {
-  var position = (e.touches && e.touches[0]) || e;
+  var position = (e.targetTouches && e.targetTouches[0]) || e;
   return {
     clientX: position.clientX,
     clientY: position.clientY
@@ -514,6 +514,11 @@ module.exports = React.createClass({
   },
 
   handleDragStart: function (e) {
+    // Set touch identifier in component state if this is a touch event
+    if(e.targetTouches){
+      this.setState({identifier: e.targetTouches[0].identifier});
+    }
+    
     // Make it possible to attach event handlers on top of this one
     this.props.onMouseDown(e);
 
@@ -574,6 +579,10 @@ module.exports = React.createClass({
   },
 
   handleDrag: function (e) {
+    // Return if this is a touch event, but not the correct one for thiss element
+    if(e.targetTouches && (e.targetTouches[0].identifier != this.state.identifier)){
+      return;
+    }
     var dragPoint = getControlPosition(e);
 
     // Calculate X and Y