Add hint to make SDL handle dbus_shutdown()

(cherry picked from commit 2348e8b6a2)

src/SDL.c

@@ -508,13 +508,13 @@ void SDL_Quit(void)
     SDL_TicksQuit();
 #endif
 
-    SDL_ClearHints();
-    SDL_AssertionsQuit();
-
 #ifdef SDL_USE_LIBDBUS
     SDL_DBus_Quit();
 #endif
 
+    SDL_ClearHints();
+    SDL_AssertionsQuit();
+
     SDL_LogQuit();
 
     /* Now that every subsystem has been quit, we reset the subsystem refcount

src/core/linux/SDL_dbus.c

@@ -186,14 +186,12 @@ void SDL_DBus_Quit(void)
         dbus.connection_close(dbus.session_conn);
         dbus.connection_unref(dbus.session_conn);
     }
-/* Don't do this - bug 3950
-   dbus_shutdown() is a debug feature which closes all global resources in the dbus library. Calling this should be done by the app, not a library, because if there are multiple users of dbus in the process then SDL could shut it down even though another part is using it.
-*/
-#if 0
-    if (dbus.shutdown) {
+
+    SDL_bool q = SDL_GetHintBoolean(SDL_HINT_SHUTDOWN_DBUS_ON_QUIT, SDL_FALSE);
+    if (q == SDL_TRUE && dbus.shutdown) {
         dbus.shutdown();
     }
-#endif
+
     SDL_zero(dbus);
     UnloadDBUSLibrary();
     SDL_free(inhibit_handle);