Committed in: changeset:   8168:3f0f4746dc7e

Manually verified that the new cookie when used under https has the prefix. However
no automated test has been created. The liveserver tests uses http and I verify
that he cookie is missing the __Secure- prefix in this case. But I have no mechanism
to create a wsgi server with an https endpoint.

Opened issue 2551373 to address this testing issue.

Also note because people could want to run a tracker on a subdomain (i.e. path != /),
the __HOST- prefix is not applicable. Also we send the domain attribute.
Hence use of __Secure-.