Merge pull request #2 from arnova/master

Just testing whether this works ;-)
fixed: Have install.sh ignore .git directories
updated: CHANGELOG
updated: arno-fwfilter with some more ports
changed: Cosmetics
fixed: A grep error would show on first run after (first) boot
changed: Only try to resolve a host once per session to speed things up in case netwerk/dns fails
changed: Cosmetics
changed: Show a warning in case host resolving fails instead of having iptables fail
fixed: Cosmetics
changed: Only try to resolve a host once per session to speed things up in case netwerk/dns fails + show warning in case host resolve fails for the traffic accounting plugin as well
changed: Plugin version bump + update CHANGELOG
Remove contrib/Gentoo directory

Gentoo-specific additions are now included and maintained in Gentoo's
portage tree.
Add systemd unit file
Fix executable path
Add check for systemd
Merge pull request #3 from ferki/remove-gentoo-dir

Remove contrib/Gentoo directory
Add comment for systemd service file installation
Merge pull request #4 from ferki/systemd

Add systemd unit file
removed: TRACE option. It's broken and there's no good way to implement it (may I suggest sh -x arno-iptables-firewall >output.file?)
changed: 'ip' function now always works with trace gone and delete a trace related README comment