Fix sim build.

Looks like older gcc (4.1.x) doesn't properly handle templated
fanciness.  Apparently that's what we have on the build server.
diff --git a/include/utils/List.h b/include/utils/List.h
index 4041a89..403cd7f 100644
--- a/include/utils/List.h
+++ b/include/utils/List.h
@@ -154,9 +154,9 @@
 
         inline _NodePtr getNode() const { return mpNode; }
 
+        _NodePtr mpNode;    /* should be private, but older gcc fails */
     private:
         friend class List;
-        _NodePtr mpNode;
     };
 
 public: