New glChess in GNOME Games

[Robert Ancell <robert ancell gmail com>]

I've just merged the Vala rewrite of glChess

Notes:
- Needs the following added to /usr/share/vala-0.12/gdk-x11-3.0.vapi:
        [CCode (cheader_filename = "gdk/gdkx.h")]
	public static X.ID x11_window_get_xid (Gdk.Window drawable);
  (Vala will hopefully update their .vapis to match GTK+3.0 soon)
- PLEASE TEST!  There will almost certainly be regressions.
- Some features are unimplemented - I think it's better to get it used
earlier rather than getting everything working.  The main missing
features are:
  - No undo
  - Captured pieces are not shown
  - Claim draw always works - the draw state needs to be implemented
  - No animations
- The GGZ networking feature is gone, it will not be re-implemented as
per the other games
- Any help is greatly welcome!