Merge remote-tracking branch 'origin/web/11374-2.9-release-notes' into doc/12001-virtualbox-needs-io-apic

It's not clear if it's needed (it might even be enabled by default) but
it's sure that it's cannot hurt.

Some future side-effect could cause unexpected behavior if applied
twice.

When trying to build Tails 2.9 with:

    TAILS_BUILD_OPTIONS="cleanall defaultcomp ram"

set, the resulting `options` string contained:

    "[...] ramcleanall [...]"

which is really bad. Fixup on this commit:

    4e8410a8 Enforce `cleanall` when building a release.

Fix-committed: #12029

Will-fix: #12029

Fix-committed: #11913

Fix-committed: #12028

This reverts commit 8c4879ea.

That change broke the "The Unsafe Browser can be used in all languages
supported in Tails" scenario because the vi_VI locale doesn't
exist. Let's solve this properly...

Merge remote-tracking branch 'origin/test/11901-mat-does-not-clean-PDF-anymore' into stable (Fix-committed: #11901)

Merge remote-tracking branch 'origin/bugfix/11965-virtualbox-5.1.8' into stable (Fix-committed: #11965)

I.e. the tests are done using a tool *different* from MAT, the tool
being tested here.

Refs: #11901

Because MAT doesn't clean PDFs anymore. :_(

Will-fix: #11901

If we have uploaded a package there we likely want it to be installable
no matter which such label it has.

Will-fix: #11965

Otherwise they are only removed from Enlgish locales. Note that the
langpacks contain copies of the English plugins, not localized versions,
so we actually do not lose nothing.