The archiver installation was a pretty simple, isolated chunk of code,
and thus easily pulled into its own script with minimal external
dependencies.
I made few changes, so the new script isn't very tidy unless it's run
from ivan.sh. It should create temp directories for anything it
downloads and clean up after itself when it's finished, but for now it
assumes ivan.sh is doing that. Mostly that's to keep the intellectual
diff small from the code in ivan.sh to the script.
I'll clean this up in an upcoming commit. Feel free to offer PRs that
do this kind of thing to other easily isolated (or not so easily
isolated) chunks. Once ivan.sh is split apart into nice logical pieces,
it will be a lot easier to test and fix individual pieces independent of
the whole. That's something we can't even say for a2server yet.
