Linkgraph: Use an arena allocator for path objects.

Fixes leaks when job is aborted early.

src/linkgraph/linkgraphjob.h

@@ -13,6 +13,7 @@
 #define LINKGRAPHJOB_H
 
 #include "../thread/thread.h"
+#include "../core/dyn_arena_alloc.hpp"
 #include "linkgraph.h"
 #include <list>
 #include <memory>
@@ -77,6 +78,8 @@ protected:
 
 public:
 
+	DynUniformArenaAllocator path_allocator; ///< Arena allocator used for paths
+
 	bool IsJobAborted() const;
 
 	/**