Merge r594839 from trunk:

core: Avoid some unexpected connection closes by telling the client
that the connection is not persistent if the MPM process handling
the request is already exiting when the response header is built.

Submitted by: trawick
Reviewed by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@596677 13f79535-47bb-0310-9956-ffa450edef68