added missing constructor; refs #7

src/mrw/checkcxx11.hxx

@@ -41,6 +41,7 @@ namespace std {
   // one from the boost library as a 1:1 replacement
   template <typename T> class shared_ptr: public boost::shared_ptr<T> {
     public:
+      explicit shared_ptr(): boost::shared_ptr<T>() {}
       explicit shared_ptr(T* p): boost::shared_ptr<T>(p) {}
   };
 };