There's now a RC of 0.3.4 packaged for Stretch, let's use it instead of
an older Git snapshot.

Merge branch 'feature/15803-tor-browser-8.0a10+force-all-tests' into testing (Fix-committed: #15803, #15706, #15801)

This reverts commit 6a35778f.

This reverts commit 284bf02c.

Tor Browser release process: clarify what to do on required libstdc++6 version bumps (refs: #15803).

Made the blueprint a bit more readable and removed the link to the secure-os email list since it's dead and no longer resolving.

Merge remote-tracking branch 'origin/feature/14481-TCRYPT-support-beta' into testing (Fix-committed: #14476).

It's been released a long time ago so is probably not very useful
at this point anymore. Besides, some more improvements are coming
in 3.9.

Merge remote-tracking branch 'origin/feature/14481-TCRYPT-support-beta' into feature/14481-TCRYPT-support-beta