Support the meta key modifier

OpenRA.FileFormats/Graphics/IInputHandler.cs

@@ -57,6 +57,7 @@ namespace OpenRA
 		Shift = 1,
 		Alt = 2,
 		Ctrl = 4,
+		Meta = 8,
 	}
 
 	public enum KeyInputEvent { Down, Up };

OpenRA.Renderer.Cg/GraphicsDevice.cs

@@ -154,6 +154,7 @@ namespace OpenRA.Renderer.Cg
 		{
 			return ( ( raw & Sdl.KMOD_ALT ) != 0 ? Modifiers.Alt : 0 )
 				 | ( ( raw & Sdl.KMOD_CTRL ) != 0 ? Modifiers.Ctrl : 0 )
+				 | ( ( raw & Sdl.KMOD_META ) != 0 ? Modifiers.Meta : 0 )
 				 | ( ( raw & Sdl.KMOD_SHIFT ) != 0 ? Modifiers.Shift : 0 );
 		}
 

OpenRA.Renderer.Gl/GraphicsDevice.cs

@@ -149,6 +149,7 @@ namespace OpenRA.Renderer.Glsl
 		{
 			return ( ( raw & Sdl.KMOD_ALT ) != 0 ? Modifiers.Alt : 0 )
 				 | ( ( raw & Sdl.KMOD_CTRL ) != 0 ? Modifiers.Ctrl : 0 )
+				 | ( ( raw & Sdl.KMOD_META ) != 0 ? Modifiers.Meta : 0 )
 				 | ( ( raw & Sdl.KMOD_SHIFT ) != 0 ? Modifiers.Shift : 0 );
 		}