Install vagrant's gettext from wheezy-backports.

Version >= 0.18.3 is a Tails build dependency nowadays.
Merge branch 'feature/vagrant-gettext-from-wheezy-backports' into stable
Merge remote-tracking branch 'origin/stable' into devel
Revert another bad use of wait_for_gnome_window().
Merge remote-tracking branch 'origin/devel' into feature/jessie