Notification of string changes

Author: Dan Poltawski
MDL-33121 book - improve a lang string
+ Make a comment match coding style


http://git.moodle.org/gw?p=moodle.git;a=commit;h=4bf433b5fbbb9a0576bc1962b762416102037011
http://github.com/moodle/moodle/commit/4bf433b5fbbb9a0576bc1962b762416102037011

+ 2.3 en [subchapternotice,mod_book]