Merge r579707 from trunk:

Ignore any ajp13 flush messages which we may mistakenly
rec' before we send the response headers. See
Tomcat PR 43478.

Reviewed by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@579999 13f79535-47bb-0310-9956-ffa450edef68