Commit d714a94d9 added support for stable xdg-shell surfaces while
preserving old unstable zxdg-shell v6 ones, but committed a mistake
in checking for both in the xdg_exporter.export error condition
paths. We want to check that the surface is neither of both.
https://gitlab.gnome.org/GNOME/mutter/issues/63Closes: #63
This commits adds support for exporting xdg_surface handles via
xdg_exporter and importing them via xdg_importer.
This bumps the required wayland-protocols version to 1.6.
https://bugzilla.gnome.org/show_bug.cgi?id=769786