Author: Andrew Robert Nicols
MDL-32142 Add missing langstring for section backups
http://git.moodle.org/gw?p=moodle.git;a=commit;h=81e33e74e09063711f7bad04defe4fa78019630b
http://github.com/moodle/moodle/commit/81e33e74e09063711f7bad04defe4fa78019630b
+ 2.1 en [backuptypesection,core_backup]