This is no GPL, but perhaps a modified MIT license
That's plain vanilla MIT, except that it says "AUTHORS" instead of "AUTHORS OR COPYRIGHT HOLDERS" in the warranty disclaimer, which is a negligible difference.
I think this should just be changed to "MIT LGPL-2+ GPL-2+", this assumes headerless files are using MIT anyway.
On a side-note, despite dead upstream, this software still works and I know a few people using it. Will have to go whenever gtk2 becomes a real problem though.