Revert "Speed improvement: Moving check online to different thread"

Temporarily reverting changes to addon_menu.cpp until they can be built on platforms other than OS X Mavericks.

This reverts commit 6d4d72e.

src/supertux/menu/addon_menu.cpp

@@ -18,7 +18,6 @@
 
 #include <config.h>
 #include <algorithm>
-#include <thread>
 #include <boost/format.hpp>
 
 #include "addon/addon.hpp"
@@ -32,12 +31,6 @@ bool generate_addons_menu_sorter(const Addon* a1, const Addon* a2)
   return a1->title < a2->title;
 }
 
-void check_online() // Shortcut to expensive function to be called by a thread
-{
-  AddonManager::get_instance().check_online();
-}
-
-
 } // namespace
 
 AddonMenu::AddonMenu() :
@@ -139,8 +132,7 @@ AddonMenu::check_menu()
   {
     try 
     {
-      std::thread addonThread(check_online);
-      addonThread.join();
+      AddonManager::get_instance().check_online();
       refresh();
       set_active_item(index);
     }