[1.5.x] Fixed #20981 -- Noted the default value of disable_existing_loggers.
[1.5.x] Fixed #20981 -- Noted the default value of disable_existing_loggers.

Backport of 095643e691 from master

imtapps/django-imt-fork,imtapps/django-imt-fork,imtapps/django-imt-fork,bliti/django-nonrel-1.5,ccn-2m/django,bliti/django-nonrel-1.5,ccn-2m/django,ccn-2m/django,bliti/django-nonrel-1.5,ccn-2m/django