So the current 2.2~rc1 thinks it is 2.2 according to "About Tails" and
`tails-version`, and adds the testing APT overlay instead of 2.2-rc1.

Bring back the dummy changelog entry for Tails 2.2 in devel.

This reverts commit b3c1d92d.

This reverts commit 2e489630.

I need to merged bugfix/11097-tor-browser-fontconfig into stable, because it
fixes a bug that affects stable. But that branch was forked off devel, so let's
revert the bits of stable..devel that we don't want on stable yet.

The removed security fixes were added to 2.0~rc1, fixing them since
2.0~beta1.

Changelog: document changes brought by jessie-p-u, and also by today's updates in stable-security and sid.