I am including these icons with oyepa under the assumption that they can be
freely distributed as long as the original authors are credited. That
assumption seems reasonable given that they are installed on my Ubuntu
system, but I admit I haven't much time trying to figure out all the details. 

The file ICON-SOURCES indicate which icon collection each individual icon belongs
to.

GNOME icons are licensed under the GPL. Cf. http://art.gnome.org

Oxygen icons are dual-licensed under the GPL and the Creative Common
Attribution-ShareAlike 3.0. Cf. http://www.oxygen-icons.org/

Humanity icons are licensed under the GPL. Cf. https://launchpad.net/humanity

Icons in the 'hicolor' collection seem to come from a variety of sources.
