E.g. if our locale is pt, which doesn't have localized search plugins,
we'll use one of pt-PT and pt-BR.

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.

... so links clicked in other applications can be opened in an already
running Tor Browser instance.

No need to copy the TBB start script's ibus stuff since it works just
fine as-is.

Instead of installing the iceweasel package (and friends) we now fetch
the TBB tarballs at build-time and extract the Tor Browser, browser
add-ons and langpacks, and browser user data into sensible places. We
try to keep something like the old organization as much as possible.

Unfortunately this drops language support to whatever subset that the
TBB supports.

- Avoid using contractions
- Say "browse the Internet"
- Use "start" instead of "launch"