filedrop: Fix file drag and drop

This fixes an issue introduced in the upgrade to jQuery three. The filedrop
field was not updated correctly and drag and drop files was broken.
Additionally, this handles cases where files are dragged over the box but
not dropped. The style of the box is correctly reset after the drag leaves
the box.

js/filedrop.field.js

@@ -11,6 +11,7 @@
       progressUpdated: $.proxy(this.progressUpdated, this),
       speedUpdated: $.proxy(this.speedUpdated, this),
       dragOver: $.proxy(this.dragOver, this),
+      dragLeave: $.proxy(this.dragLeave, this),
       drop: $.proxy(this.drop, this),
       beforeSend: $.proxy(this.beforeSend, this),
       beforeEach: $.proxy(this.beforeEach, this),
@@ -29,6 +30,9 @@
   };
 
   FileDropbox.prototype = {
+    dragLeave: function(e) {
+        this.$element.removeAttr('style');
+    },
     drop: function(e) {
         this.$element.removeAttr('style');
     },
@@ -361,9 +365,9 @@
 
     function drop(e) {
       if( opts.drop.call(this, e) === false ) return false;
-      if(!e.dataTransfer)
+      if(!e.originalEvent.dataTransfer)
         return;
-      files = e.dataTransfer.files;
+      files = e.originalEvent.dataTransfer.files;
       if (files === null || files === undefined || files.length === 0) {
         opts.error(errors[0]);
         return false;