Author: Paul Holden
MDL-82444 filter_tidy: advertise required PHP extension.
http://git.moodle.org/gw?p=moodle.git;a=commit;h=90fa52089e207dd4100db830e9c2975bce5d297f
http://github.com/moodle/moodle/commit/90fa52089e207dd4100db830e9c2975bce5d297f
+ 4.3 en [tidyextensionrequired,filter_tidy]