I'm attaching a code patch and an ebuild patch to make xinerama support optional in gtk2. I haven't sent it upstream, as I'd prefer that someone who knows GTK (and upstream) better can evaluate this before. HTH, Diego
Created attachment 76887 [details, diff] Ebuild patch
Created attachment 76888 [details, diff] gtk+-2.8.9-xinerama.patch
Fixed in gtk+-2.8.10