xwm: Plug kill signal for killing X apps

Xeyes is the counter-example that fails on that heuristic and won't be caught
on kill binding. This and the last two patches should fix:

    https://bugs.freedesktop.org/show_bug.cgi?id=53679

Signed-off-by: Tiago Vignatti <tiago.vignatti@intel.com>
diff --git a/src/xwayland/xwayland.h b/src/xwayland/xwayland.h
index bd127b7..a1ffa2a 100644
--- a/src/xwayland/xwayland.h
+++ b/src/xwayland/xwayland.h
@@ -63,6 +63,7 @@
 	int last_cursor;
 	xcb_render_pictforminfo_t format_rgb, format_rgba;
 	struct wl_listener activate_listener;
+	struct wl_listener kill_listener;
 
 	xcb_window_t selection_window;
 	xcb_window_t selection_owner;
@@ -85,7 +86,9 @@
 		xcb_atom_t		 wm_delete_window;
 		xcb_atom_t		 wm_state;
 		xcb_atom_t		 wm_s0;
+		xcb_atom_t		 wm_client_machine;
 		xcb_atom_t		 net_wm_name;
+		xcb_atom_t		 net_wm_pid;
 		xcb_atom_t		 net_wm_icon;
 		xcb_atom_t		 net_wm_state;
 		xcb_atom_t		 net_wm_state_fullscreen;