fixed detection of secure cookies received over https

BrowserKit's cookie handling only recognises a secure cookie if the
cookie option is set and the cookie was set over an https request.
The client was not passing the url into the cookiejar update code,
causing Cookie::isSecure() to always return false for every cookie.

Fixes symfony/symfony#7666
[BrowserKit] removed dead code
[HttpFoundation][BrowserKit] fixed path when converting a cookie to a string

An empty path has a different meaning than a /; it means that the path
is the one from the current URI.