Mouse: Optimize the cancel locator, works around a bug where .add(event.target) in IE8 can take a long time when there are multiple siblings. Fixes #7118 - IE Bug Large ComboBox (Dialog)

(cherry picked from commit 09e88d6)

Author: Jay Merrifield

ui/jquery.ui.mouse.js

@@ -58,7 +58,7 @@ $.widget("ui.mouse", {
 
 		var self = this,
 			btnIsLeft = (event.which == 1),
-			elIsCancel = (typeof this.options.cancel == "string" ? $(event.target).parents().add(event.target).filter(this.options.cancel).length : false);
+			elIsCancel = (typeof this.options.cancel == "string" ? $(event.target).closest(this.options.cancel).length : false);
 		if (!btnIsLeft || elIsCancel || !this._mouseCapture(event)) {
 			return true;
 		}