Cookies: Don't override cookies with outdated values

[TheOneRing]

This code was actually not breaking most cookie handling by accident.
As the raw cookies where not split properly we added cookies with values like
"key: val; key2 = val2; key3 = val3"
When the code was corrected we overwrote the newer values in the jar with
the old ones from a request.

[ogoffart]

The code must have been like this for a reason... But i cannot remember why (maybe @guruz knows)

[TheOneRing]

The code was introduced in b037e63

And it can never have worked when more than one cookie was set.
And with that code fixed, it was possible that we received a new cookie in a reply, and overwrote it with the old one.

[guruz]

I don't remember why, but if we later can confirm that the client still works in setups where there is some cookie-based sticky load balancing then i'm fine with it CC @HanaGemela

[HanaGemela]

@TheOneRing @guruz Please provide steps to test

[TheOneRing]

We don't really have a test case for this besides running the client with any server.
As this seems to work and the patch fixed the client behaviour with a more complex cookie setup (f5) I expect it to work.