Guard against allowing intermediate caching when cookies are present
Output cache-control headers that disable intermediate caching even if
OutputPage->mEnableClientCache is true when the response includes
set-cookie headers as well. This change mirrors logic that has been in
use on the Wikimedia Foundation production cluster's Varnish cache
system for over 2 years to guard against accidentally caching backend
responses which include Set-Cookie headers.
Co-Author: Max Semenik <email@example.com>