QA: make use of override instead of virtual for method overrides
[plugins] director: minor code refactors
[http] HttpServer: now always logs logging severity change
[plugins] director: fcgi backend now uses std::unique_ptr<> to guard socket to backend (QA)
ChangeLog update
[plugins] director: don't override response status on fcgi EndRequest message
[plugins] director: RoadWarrior::reject() to only set response status if not already done
[base] CustomDataMgr: make use of std::forward<T>()
[contrib] high-traffic-linux.sh: minor hint on errno
config file update
config file update
[plugins] director: major code refactorization of the FastCGI backend implemenation in order to void reference counts.

The new implementation associates the backend connection object as a
custom data object to the request it is to handle.
So we get automatically removed when we invoke request->finish().
coding style adaptions