that branch upgrades Tor Browser to the candidate 4.0.5 build
provided by GeKo. Please review, test and merge into stable.
(Same is for Tor 0.2.5.11: I've not tested it yet, will start doing
that shortly, and may have to merge myself in order to avoid delaying
the emergency release => let's please coordinate on #tails-dev if you
want to help.)
