AFL-2.1: Add optional appendix

[castholm]

dbus is probably one of the most prolific projects licensed under AFL-2.1 and their original AFL 2.1 license text had an appendix (similar to the last part of GPL licenses) which ironically was lost when they made their repository REUSE-compliant and used REUSE's tooling to replace the license with the license text downloaded from this very repository!

I replaced the test license text with the license text from dbus, since it appears to be the most complete reproduction of the original AFL 2.1 license text. Apologies in advance to any maintainers for the change in text wrapping.

Additionally, both the dbus license text and the text in https://web.archive.org/web/20061013013632/http://opensource.linux-mirror.org/licenses/afl-2.1.txt has a space between the "v." and the "2.1". But because the license text from this repo has already proliferated, we can't correct the mistake outright and have to accept both a space and no space.

[jlovejoy]

@castholm - sorry! This got a bit lost in the shuffle. Did you make an issue explaining this or just this PR?

I think this is ONLY adding the explanation part after the END OF LICENSE - this text was not in the original AFL-2.1, but was and is included in dbus, so you want to add it here as optional so the dbus variant will still match to AFL-2.1.- is that right?

I'm not sure this is necessary, as it's clearly not part of the license given it's after the END OF LICENSE text??

[castholm]

@jlovejoy I didn't open an issue beforehand, I only made this PR when I was consolidating license information for a project that vendors files from lots of different projects and noticed some discrepancies.

It's difficult to verify whether the original AFL-2.1 license text included the explanation after END OF LICENSE or not since there's no surviving canonical source. However, some reproductions of AFL-1.1 and AFL-1.2 did include that explanation. And for whatever reason, the dbus project then included this explanation from 1.1/1.2 in their 2.1 license text (note that the appendix still mentions "version 1.0") which caused it to proliferate.

Either way, my point is that there are reproductions of the AFL-2.1 license text floating around that include this END OF LICENSE appendix (quick example I found by searching GitHub), so I thought it might be good to include it for improved matching and for posterity. The XML file for GPL includes the "END OF TERMS AND CONDITIONS" part so I don't see why AFL would be any different if the appendix is commonly included with the license text.