Git commits in Moodle 3.3.x by Helson Castro

commit 5ad0bb82f177aed7f2fb909d5a0c6c5b078f36c9
Author: Helson Castro <helsonaraujo@hotmail.com>
Date:   Fri, 27 Jan 2017 13:55:07 +0800
Tag:    v3.3.0-beta

MDL-57568 forms: Added missing include for button element.