Merge r571002 from trunk:

proxy_http: don't wait for response body in a HEAD
PR 41644 [Stuart Children]

Submitted by: niq
Reviewed by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@571777 13f79535-47bb-0310-9956-ffa450edef68