Merge r571338 from trunk:

mod_proxy: Add Proxypass status option to ignore errors
PR 43167.  Patch by Francisco Gimeno

Submitted by: niq
Reviewed by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.2.x@571778 13f79535-47bb-0310-9956-ffa450edef68