Author: Nicolas Dunand
MDL-26017 enrol: Add keyholder role
http://git.moodle.org/gw?p=moodle.git;a=commit;h=0ac6a57ec5a6a2be9d5f2fc13e2dae5ac0321d4c
http://github.com/moodle/moodle/commit/0ac6a57ec5a6a2be9d5f2fc13e2dae5ac0321d4c
+ 2.9 en [keyholder,enrol_self]
+ 2.9 en [self:holdkey,enrol_self]