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According to NetworkManager(8) IP4_NAMESERVERS is a space separated
list.

We still do it for `try_for()` blocks, since they quite quickly can
puke out screenfulls of errors.

So it's not confused with Tor Browser's default search eninge,
Startpage.

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.