Author: Andrew Davis
MDL-43188 core_message:reimplemented the beep on new message functionality from 1.9
http://git.moodle.org/gw?p=moodle.git;a=commit;h=c8d061208d5b0d4d3bd4f8ef36190a8d8bfcecb2
http://github.com/moodle/moodle/commit/c8d061208d5b0d4d3bd4f8ef36190a8d8bfcecb2
+ 2.4 en [beepnewmessage,core_message]