I just uploaded a revised version of the Lua plugin that should be compatible with Geany 0.12 and GTK 2.8 through 2.12.
As per Murphy's Law, the hosting service where I had the files stored disappeared from the face of the Earth at almost the same instant that Enrico announced Geany-0.12!
But I have since moved the files to a different server, so hopefully all is well now. If you have had trouble downloading them in the past few days, please try again now: http://yetanothergeek.justfree.com/geanylua/
Regards, - Jeff