Make closeWindow() a public slot

For JavaScript bindings.

client.h

@@ -468,7 +468,6 @@ public:
     void setMinimized(bool set);
     void minimize(bool avoid_animation = false);
     void unminimize(bool avoid_animation = false);
-    void closeWindow();
     void killWindow();
     void maximize(MaximizeMode);
     void toggleShade();
@@ -566,6 +565,9 @@ public:
     //sets whether the client should be treated as a SessionInteract window
     void setSessionInteract(bool needed);
 
+public slots:
+    void closeWindow();
+
 private slots:
     void autoRaise();
     void shadeHover();