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It makes a bit of sense on its own, and it guarantees that no weird
cruft in ~/.tor-browser will interfere for whatever reason.

No code is deleted/added/modified, only moved.

We could use `cp --no-dereference` before, when the TBB_EXT dir only
contained symlinks. This will reduce the memory footprint of the
chroot browsers, and incidentally fixed a bug where the
unsafe-browser's name wasn't set since we copied the langpack before
we fix the name in it.

We don't have to any more (after the TBB migration) since we
explicitly set up the ones we want to use. This should speed up the
start and reduce the memory footprint.

And use it consistently in all places instead of using the value as a
magic constant.

Extracting and then compressing the whole langpack/omni.ja isn't
necessary and takes a lot of time. Tests show a 50% reduction in
startup time.

After installing incremental upgrades Tails' root filesystem consists
of a stack squashfs:s, not only filesystem.squashfs. When not stacking
them correct we may end up using the Tor Browser (Firefox) from an
older version of Tails, or with no Tor Browser at all, as in the
upgrade from Tails 1.1.2 to 1.2, when we migrated from Iceweasel to
the Tor Browser.

Based on patch contributed by sanic.

It was added by mistake when adapting the script for the
TBB-migration.

It was a relic of the TBB 3.x times when the profile was located in
the parent directory of the TBB browser files.

Also patch Tails Greeter with the updated path. That patch should
be dropped once it's been upstreamed into Tails Greeter.

That way one only has to remember to always call firefox with
exec_firefox(), and not to set LD_LIBRARY_PATH. As an example, this
was forgotten for Tor Launcher, which also was fixed.

The libstdc++6.so we have (from Debian Wheezy) is too old.