More spelling fixes from debian's lintian.
Reword the reference to the GPL in the manpage.

lintian didn't like "Gnu" instead of "GNU", and the wording was a
little off, to me.
Fix a copy and paste typo in LICENSES.
Replace "or later" text in LICENSES with "+"

This will reduce column size, which can be an issue for dual-licensed assets.
Mark assets entirely from Bertram and Allacrost as GPLv2+.

I think this is what they intended, since that's what's in the COPYING
file.
Mark GPLv2 assets from The Mana World as GPLv2+.

That appears to be the intent for their project, since that's how the
code is licensed.
Clarify that the ',' for OGA licenses is "or" (dual-licensed).

Things are probably simpler than this -- for artists, OGA has a
checkbox for marking the "or any later version" text, but that appears
to not be presented to people browsing the site!
The Linux Libertine fonts are dual-licensed.

Debian packaging claims it's v2+, and at this point upstream points to
stock GPLv3 for that license.
Update licensing info for a composite asset.

This one looked suspicious to me since it didn't note the licenses for
the mixed in components, and indeed it looks like there's a conflict.
Mark mapeditor.org as GPLv2+.

The code next to this art is "or any later version" in the upstream
tree.
Add more detailed information on the source of growl1.
Separate the COPYING file into a v2 and a v3 copy.

The v3 copy came from /usr/share/common-licenses/GPL-3 on my debian system.
Add copies of the CC licenses used by some of our art assets.

I took the copies of the CC-BY-3 and CC-BY-SA-3 text from debian's
copyright file for freedesktop-sound-theme, and the CC0 text I grabbed
from creativecommons.org and formatted it myself.
Merge pull request #213 from anholt/for-upstream

Licensing information improvement.

Thanks a lot to @anholt for the hard work. :)