bug1019528 - use of cachecontrol

https://bugzilla.mozilla.org/show_bug.cgi?id=1019528
Another thing, I know that was my in proposition to define the method like:
set_http_cache_session(http_cache_dir=None, ...)
But I changed my mind and would prefer set_http_cache_session(cache_session)
This way we could disable it by passing None, and it will be the responsibility of the caller to give a configured instance of a cacheControl.