add eoStoreFunctor::pack to allocate & store in one line

Instead of calling `new`, then `state.storeFunctor`, the user can just call
`Class& inst = state.pack< Class >( params )` in one line.

Use C++11's variadic templates.

eo/src/eoFunctorStore.h

@@ -69,6 +69,22 @@ public:
         return *r;
     }
 
+    /** Allocate the given functor, store it and return its reference.
+     *
+     * Indicate the class to instanciate as template paramater,
+     * and pass its constructor arguments.
+     *
+     * @code
+     * eoSelect<EOT>& selector = state.pack< eoRankMuSelect<EOT> >( mu );
+     * @endcode
+     */
+    template<class Functor, class... Args>
+    Functor& pack( Args&&... args )
+    {
+        Functor* f = new Functor(args...);
+        return this->storeFunctor(f);
+    }
+
 private :
 
     /** no copying allowed */