Set up window focus correctly when using an existing X11 window.

Thanks to Joseph Toppi for the fix!

--HG--
extra : rebase_source : be4596056669a0a9c7580355084b7f9eca345d78

src/video/x11/SDL_x11window.c

@@ -191,6 +191,21 @@ SetupWindowData(_THIS, SDL_Window * window, Window w, BOOL created)
         }
     }
 
+    {
+        Window FocalWindow;
+        int RevertTo=0;
+        XGetInputFocus(data->videodata->display, &FocalWindow, &RevertTo);
+        if (FocalWindow==w)
+        {
+            window->flags |= SDL_WINDOW_INPUT_FOCUS;
+            SDL_SetKeyboardFocus(data->window);
+        }
+
+        if (window->flags & SDL_WINDOW_INPUT_GRABBED) {
+            /* Tell x11 to clip mouse */
+        }
+    }
+
     /* FIXME: How can I tell?
        {
        DWORD style = GetWindowLong(hwnd, GWL_STYLE);