Merge r1809273, r1814719 from trunk:

event: better apr_pollset_add() failure handling to avoid an (very unlikely)
worker vs listener race condition.



Follow up to r1809273: CHANGES entry.


Submitted by: ylavic
Reviewed by: ylavic, jim, covener


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1818963 13f79535-47bb-0310-9956-ffa450edef68