wayland: Support for QtWayland surface extension

Add support for the surface_extension protocol from QtWayland,
with qt_surface_extension and qt_extended_surface interfaces.

Right now, this only adds support for handling "close" events on
windows, but other features (windowflag / OverridesSystemGestures)
could be implemented using this integration in the future.

The files wayland-qt-surface-extension.{c,h} are auto-generated
from the XML definition src/extensions/surface-extension.xml in
qtwayland (git://gitorious.org/qt/qtwayland.git).
Merge pull request #20 from thp/wayland-surface-extension

wayland: Support for QtWayland surface extension