Add security discussion wrt. running syslinux from the upgraded system.
Merge remote-tracking branch 'origin/testing' into bugfix/7345-upgrade-from-iso-from-1.0-to-1.1
Drop painful manual run of pherkin tests: now integrated via t/10-features.t.

Oh, and the Cucumber test suite was fixed to nicely clean up loop devices
and mounts after itself :)
Make it clear that ideally, we would use the right version of tails-perl5lib when building tails-iuk.
Merge branch 'bugfix/7345-upgrade-from-iso-from-1.0-to-1.1' into devel
Merge branch 'devel' into experimental