Added include <cstdlib> for using 'NULL' (apparently gcc 4.6 is more strict)

src/contrib/graphbuilderadapter.h

@@ -5,6 +5,7 @@
 #pragma once
 #endif
 
+#include <cstdlib>
 #include <map>
 #include <stack>
 #include "yaml-cpp/eventhandler.h"

src/ptr_stack.h

@@ -6,6 +6,7 @@
 #endif
 
 #include "yaml-cpp/noncopyable.h"
+#include <cstdlib>
 #include <memory>
 #include <vector>
 

src/ptr_vector.h

@@ -6,6 +6,7 @@
 #endif
 
 #include "yaml-cpp/noncopyable.h"
+#include <cstdlib>
 #include <memory>
 #include <vector>