Add include for string.

The .cpp complains about sort... still looking for a fix for that.


git-svn-id: svn+ssh://svn.code.sf.net/p/supertuxkart/code/main/trunk@10328 178a84e3-b1eb-0310-8ba1-8eac791a3b58

src/tracks/lod_node_loader.hpp

@@ -26,6 +26,7 @@ class LODNode;
 
 #include <map>
 #include <vector>
+#include <string>
 
 namespace irr 
 {