[1.6.x] Fixed #15582 -- Documented how TransactionTestCase.multi_db affects fixtures.
[1.6.x] Fixed #15582 -- Documented how TransactionTestCase.multi_db affects fixtures.

Thanks slinkp for the suggestion.

Backport of dd839a2dfd from master

felixjimenez/django,felixjimenez/django,django-nonrel/django,redhat-openstack/django,django-nonrel/django,redhat-openstack/django,django-nonrel/django,dex4er/django,felixjimenez/django,redhat-openstack/django,dex4er/django,django-nonrel/django,felixjimenez/django,redhat-openstack/django,dex4er/django