Bug#663749: enable wayland backend

[darxus at chaosreigns.com]

I believe this will require re-enabling cairo-gl, temporarily disabled
a year ago:

cairo (1.10.2-5) unstable; urgency=low
 -- Emilio Pozuelo Monfort <pochu at debian.org>  Fri, 25 Mar 2011 22:10:28 +0000
    + Temporarily disable the OpenGL/EGL backend, since that makes us
      block on mesa / libdrm / linux-2.6 to migrate to testing, and 
      we're blocking the gobject-introspection transition, and we don't
      want to tie them. It will be re-enabled soon after we migrate.