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
[HttpFoundation] fixed empty domain= in Cookie::__toString()
[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.
merged branch fabpot/cookie (PR #7738)

This PR was merged into the 2.1 branch.

Discussion
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[BrowserKit] fixed detection of secure cookies received over https

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #7666, #7738
| License       | MIT
| Doc PR        | N/A

As reported in symfony/symfony#7666, 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.

I have corrected this behaviour and added an additional unit test to prove the bug and fix.

Commits
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36d057b [HttpFoundation][BrowserKit] fixed path when converting a cookie to a string
c884151 [BrowserKit] removed dead code
495d0e3 [HttpFoundation] fixed empty domain= in Cookie::__toString()
c2bc707 fixed detection of secure cookies received over https