Author: David Mudrák
MDL-51261 admin: Support upgrade key requirement on the site upgrade
The upgrade key can be defined in the main config.php as
$CFG->upgradekey. If it is defined there, then its value must be
provided every time the site is being upgraded, regardless the
administrator is logged in or not.
http://git.moodle.org/gw?p=moodle.git;a=commit;h=98b32c9e7ed92fede5e7c277aac2d3e255f2f0f3
http://github.com/moodle/moodle/commit/98b32c9e7ed92fede5e7c277aac2d3e255f2f0f3
+ 3.0 en [upgradekeyreq,core_admin]