Author: Tim Hunt
MDL-20636 Add warning about very old attempts to listpreupgrade.php.
http://git.moodle.org/gw?p=moodle.git;a=commit;h=d02ac70862a98d944b17242796e038ebdbf58463
http://github.com/moodle/moodle/commit/d02ac70862a98d944b17242796e038ebdbf58463
+ 2.1 en [listpreupgradeintro,local_qeupgradehelper]