Disabledif JavaScript is very inefficient

Note This patch changes javascript libraries, so be sure to purge caches and do a browser shift-reload after applying. Performance testing: Copy the attached bigform_test.php to the moodle root and visit with a browser. It will be very slow to load and handle events. With the patch it's much faster. Regression testing: This needs to be tested on as many browsers as possible. Some good pages to test: attached bigform_test.php (copy to moodle root) Each form group contains an Enable checkbox which enables/disables the entire group. Verify that this interacts properly with the datetime control enable boxes. attached samstest.php (copy to moodle root) In particular, verify that nested dependencies work properly: In the "Disabled if things change" section: Unchecking "Test checkbox" should disable the Basic and Array groups. Clearing the text in the first textfield should disable the Basic and Array groups. Adding text to the second textfield should disable the Basic and Array groups. Changing the select to "No" should disable the Basic and Array groups. In the Stacked Chain, each item disables/enables all the items below it. For the Date/Duration selectors, the enable box should enable/disable the entire selector. Other moodle pages: Backup UI XML Grade upload Calendar event add Forum settings page Assignment settings page