Notification of string changes

Author: Petr Škoda
MDL-28980 add basic expiry notification support to manual enrolments
Thanks Helen Foster for the lang string improvements.


http://git.moodle.org/gw?p=moodle.git;a=commit;h=129e6d36a477b8bfafbeef45084872e0de7dee1a
http://github.com/moodle/moodle/commit/129e6d36a477b8bfafbeef45084872e0de7dee1a

+ 2.4 en [errorthresholdlow,enrol_manual]
+ 2.4 en [expirymessageenrollersubject,enrol_manual]
+ 2.4 en [expirymessageenrollerbody,enrol_manual]
+ 2.4 en [expirymessageenrolledsubject,enrol_manual]
+ 2.4 en [expirymessageenrolledbody,enrol_manual]
+ 2.4 en [expirynotify,enrol_manual]
+ 2.4 en [expirynotify_help,enrol_manual]
+ 2.4 en [expirynotifyall,enrol_manual]
+ 2.4 en [expirynotifyteacher,enrol_manual]
+ 2.4 en [expirythreshold,enrol_manual]
+ 2.4 en [expirythreshold_help,enrol_manual]
+ 2.4 en [messageprovider:expiry_notification,enrol_manual]
+ 2.4 en [notifyhour,enrol_manual]