Fix compiling in release

git-svn-id: svn+ssh://svn.code.sf.net/p/supertuxkart/code/main/trunk@12643 178a84e3-b1eb-0310-8ba1-8eac791a3b58

src/challenges/unlock_manager.cpp

@@ -34,6 +34,7 @@
 #include "karts/kart_properties_manager.hpp"
 #include "race/race_manager.hpp"
 #include "tracks/track_manager.hpp"
+#include "utils/log.hpp"
 #include "utils/string_utils.hpp"
 
 UnlockManager* unlock_manager=0;