Merge r986591 from trunk:

Don't log errors when we can't send to client, just debug.

Submitted by: jfclere
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@989125 13f79535-47bb-0310-9956-ffa450edef68