Silence gcc warnings when using UnaryFunction with reference parameters.

[SVN r61152]

include/boost/concept_check.hpp

@@ -330,7 +330,15 @@ namespace boost
       {
           f(arg);
       }
-      
+
+#if BOOST_WORKAROUND(__GNUC__, BOOST_TESTED_AT(4))
+      // Declare a dummy construktor to make gcc happy.
+      // It seems the compiler can not generate a sensible constructor when this is instantiated with a refence type.
+      // (warning: non-static reference "const double& boost::UnaryFunction<YourClassHere>::arg"
+      // in class without a constructor [-Wuninitialized])
+      UnaryFunction();
+#endif
+
       Func f;
       Arg arg;
   };