MEDIUM: http: Ignore http-pretend-keepalive option on frontend

This option is backends specific, so there is no reason to support it on
frontends. So now, it is ignored if it is set on a frontend and a warning is
emitted during the startup. The change is quite trivial, but the commit is
tagged as MEDIUM because it is a small breakage with previous versions and
configurations using this options could emit a warning now.
2 files changed