Add the ability to exit the game using escape.

osu.Game/GameModes/Menu/ButtonSystem.cs

@@ -125,6 +125,15 @@ public override void Load()
 
         protected override bool OnKeyDown(InputState state, KeyDownEventArgs args)
         {
+            if (args.Key == Key.Escape)
+            {
+                if (State == MenuState.Initial)
+                    return false;
+
+                State = MenuState.Initial;
+                return true;
+            }
+
             osuLogo.TriggerClick(state);
             return true;
         }

osu.Game/GameModes/Menu/Intro.cs

@@ -66,5 +66,16 @@ protected override void OnSuspending(GameMode next)
             Content.FadeOut(300);
             base.OnSuspending(next);
         }
+
+        protected override void OnResuming(GameMode last)
+        {
+            //this is an exit
+            Game.Scheduler.AddDelayed(delegate
+            {
+                Game.Exit();
+            }, 300);
+
+            base.OnResuming(last);
+        }
     }
 }

osu.Game/GameModes/Menu/MainMenu.cs

@@ -49,7 +49,7 @@ public override void Load()
                             OnTest  = delegate { Push(new TestBrowser()); },
                             OnExit = delegate {
                                 Game.Scheduler.AddDelayed(delegate {
-                                    Game.Host.Exit();
+                                    Exit();
                                 }, ButtonSystem.EXIT_DELAY);
                             },
                             OnSettings = delegate {