* Set Max-Age= flag instead of Expires= flag.
* Set Secure flag when using HTTPS.
* Extend default cookie lifetime from 1 year to 20 years.
* Remove "session" expiration option (unused).
* Remove max cookie size check.
The cookie size check was previously added in #2518 to deal with running
out of space due to tag scripts and blacklists. This should no longer
happen since we no longer use cookies for these things. Remove the
warning because it should never happen, we can't fix it if it does, and
the user probably won't know how to fix it either.
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