Merge r377053, r377057 and r377525 from trunk, fixing several issues with...

Merge r377053, r377057 and r377525 from trunk, fixing several issues with mod_proxy_http and keep-alive headers.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@390608 13f79535-47bb-0310-9956-ffa450edef68